0> MAGNETIC OBSERVATIONS AT AND NEAR ALBANY, N. Y., BETWEEN THE YEARS 1686 AND 1892. By Vkrplanck Colvin.i/" # MAGNETIC OBSERVATIONS AT AND NEAR ALBANY, N. Y., BETWEEN THE YEARS 1686 AND 1892. By Verplanck Colvin. ^^ [Read before the Albany Institute, January 4,1888; Revised to December 1,1892.] Physical science affords no more interesting phenomenon than ter- restrial magnetism. An invisible, yet potent omnipresent force, it is as important in its functions as is gravitation; and may, indeed, be a form or mode of energy supplementary to that greater power by which rivers run their courses downward to the sea. Terrestrial magnetism, however, differs from gravitation in being, even locally, an inconstant force; varying in accordance with its own local laws, and controlled by causes as yet little understood; yet penetrating and traversing even the massive mountains which gravitation holds so rigidly in place. Every one appreciates the all-pervading nature of gravitation. Under its control the snow flakes fall steadily and regularly toward the earth. In obedience to gravitation the torrent of Niagara pours con- tinuously into its gulf; and, at the command of this invisible force the Moon pursues the World ; while the most distant planets, in their courses, majestically keep the orbits which the laws of gravitation pre- scribe. When, after studying the wonderful symmetry and system of this great force, we encounter another mode of energy in matter, with an influence extending not only throughout the World hut also — in all probability — throughout the Universe; associated with the phenom- ena of light, heat and electricity; we cannot but believe that this, the so-called terrestrial magnetism, is a condition of energy in matter that might be called, with better reason, Cosmical Magnetism; the natural magnetism of matter in space; and as much a portion of the celestial mechanism as gravitation itself. It is true that the force controlling magnetism is, like electricity, invisible. When we speak of magnetism we refer to the reaction of this invisible force upon visible magnetic bodies; the substances we 2 Magnetic Observations. call magnets, or those bodies susceptible to magnetism; and, by ob- serving the varying movements of these bodies — suspended or other- wise so placed as to be free to the magnetic influence— we write down these movements, record the changes of pointing, trace the curves of motion, and find the intensity; until, by thus watching bodies controlled by the magnetic influence, we form some opinion of the invisible force that occasions these movements. Thus, with the aid of the various forms of magnetometer, we obtain mental concepts; ideals of the geometry of magnetic lines in space which, when systematized, may enable us, from a knowledge of the past events in terrestrial mag- netism, to make predictions of future occurrences that will be of great.benefit to mankind. If for the theoretical " Ether" of school philosophies we substitute the idea of a ubiquitous multi-mode energy; ever existent in some ratio to matter, however infinitesimally attenuated this matter may be; we conceive an energy capable of an infinite variety of reactions, in accordance with the position or form of matter affected by it, and by this idea may arrive at a better conception of the nature of the phe- nomena of magnetism. Nor is this the only useful result of this modification of theory; for this conception of the energy of space, if it agree more closely and rationally with the facts of nature, may also, perhaps, account for all the so-called "physical forces/' as resultants of the reactions of the diffused energy of space on the various local as- pects of energy and matter. It is not the purpose of the present paper, however, to consider or investigate the existence of a primal form of energy Avhich shall re- place in physical theory the "Ether" of the speculative philosophers. My views on this subject are already before the Institute. The object of the present paper is to make public some new local magnetic data, Avith notices of other and more ancient records, which have hitherto escaped notice. It is thought best to accompany these observations with some calculations, which I have made by the formula considered by the chief mathematician of the United States Coast Survey the closest approximation so far made to the law of the magnetic declination at Albany, as a means of predicting the positions of the compass needle through its secular movement for many years to come. By comparing the computed predictions with the actual variation observed, not only is an idea had of the accuracy of this method of pre- diction — and, vice versa, of the irregularities in the actual movement of the needle as observed — but some notion also will be had of what is being sought by students of terrestrial magnetism, while the column of Magnetic Observations. 3 differences, between the observations and predictions, will give an idea of the present degree of progress in this department of scientific research. While avoiding, in this paper, any lengthy discussion of the nature of the energy of space; of force per se; as the cause of magnetic ac- tion; it is proper to call to mind some of the phenomena which, from their close connection with this subject, have made the expressions Terrestrial Magnetism and Cosmical Magnetism appear to be the proper titles for this branch of research. The telescopic study of the Sun has shown that enormous disturb- ances of the solar atmosphere occur at times. Magnetic observations made upon the Earth, at moments identical with those of the solar disturbance, show that such solar action is synchronous with intense magnetic action at terrestrial stations. While we cannot prove that the solar disturbance is the cause of the magnetic disturbance upon the Earth, yet there appears to be a magnetic bond between the Sun and the Earth, through the apparently open intervening space, with a probability that the Sun is more nearly the centre of the origin, and the Earth the location of a resultant of the magnetic disturbance. It is from this phenomenon that we obtain the mental concept of a primary or Solar magnetism, and a secondary or Terrestrial magnetism. It is a logical sequence of the instantaneous communication through space, of this mysterious influence, that there must be an energy and magnetism in space or Cosmical Energy or Cosmical Magnetism; an atmosphere of force, Avhich probably controls both the magnetism of the Sun and its planets. Hence by terrestrial magnetism is meant the magnetic atmosphere of the Earth; and "magnetic observations " are observations of the local action of this so-called atmosphere upon matter; the record giving an account of the visible movements of sensitively arranged magnets, or matter sensitive to magnetism, under the influence of this assumed magnetic atmosphere. The " magnets " of the magneto- meters, or declinometers, are indices from whose movements we are able to form some opinion of the invisible, magnet-making Energy, the powers of which we seek to understand from its functions, by gauging, measuring or weighing its action on matter sensitive to its influence. In every case the observations at any particular locality afford only what may be called a knowledge of the local magnetism; or, more properly — for we have no brief name for it — the condition of the cosmic magnetic energy, under the local influences. 4 Magnetic Observations. It is to such observations of the local magnetic conditions at Albany, N. Y., at a great number of dates during the past two hundred years, that I desire to call your attention; and I particularly invite your at- tention to the record given of observations prior to the year 1817. Though these observations are few in number; only nine having been preserved between the years 1686 and 1807; yet they contain the most important date of the epoch of the maximum easterly movement of the magnetic needle at Albany, the observation nearest to this period hav- ing been made by the Surveyor-General of this State, Simeon De Witt, in the year 1805. The degree of maximum easterly movement, which is also the minimum westerly declination of the needle, was found by General De Witt to be +4° 58' west of north from the true meridian at Albany on the 30th day of July, 1805. This result is so different from the value of the declination assigned to this date by theory, that I have been at great pains to see whether other and corroborating data could not be found. In this I have been successful; and, from records left by the late Prof. Joseph Henry, have found the declination in 1798 to have been +5° 00' West of true North- which fully corroborates the view of General De Witt that the easterly movement of the magnetic needle at Albany continued until about the year 1805 (or 1807) and then suddenly changed to an annual westerly movement. That previously to this date, the magnetic needle at Albany had a continuously easterly movement, I have been able to satisfy myself from other data, of early surveys of the land patents in the vicinity of Albany. This unpublished data shows that in the year 1686 the magnetic declination at Albany was D = + 9° 09' (North- west); in 1735, D = + 7° 40' (North-west) ; in 1768 D = + 6° 39' (North-west); in 1787, D = + 5° 03' (North-west); in 1789, D = + 5° 27' (North-west); in 1798, D = + 5° 00' (North-west); in 1805, D = + 4° 58' (North-west); indicating a decrease of declination as the year 1805 is approached; or a continuous easterly movement of the magnetic needle, as claimed by Surveyor-General De Witt, in his record of April 27th, 1825. The fact that these more ancient observations differ entirely from what the present theory of local magnetism would indicate, makes them of the greatest importance as the key to a more accurate theory of the period and extent of the alternative progression and retrogres- sion or secular movement of the magnetic force at Albany. To this collection of ancient observations, I have added all those which are comparatively well known, so as to bring together all the data, of value for this investigation, in one paper. Magnetic Observations. 5 The new data, being the observations at Albany of the magnetic declination between the years 1874 and 1892, are my own observations and are now for the first time made public. My station of observation has been in the grounds of my residence on Western avenue in this city, and is marked by monuments and ref- erence points which may hereafter be found and identified by means of the accompanying diagram. The magnetic station is marked by a brown-stone monument having a copper-plug, with cross, set as centre. 6 Magnetic Observations. In the diagram the central circle is the brown-stone monument of the magnetic station; the other circles near this central station are the limestone piers of the astronomical instruments. The geodetic coordinates of the brownstone monument are Latitude = 42° 39' 43". 63. Longitude, in arc = 73° 46' 33".48. " in time = 4h. 55m. 06.23s. W. from Greenwich. Altitude = 227 -]Y^j-th ^eet above mean tide level. While there are several phases of the magnetic phenomena, usually investigated at permanent stations; as the intensity with which it affects magnetic matter, the dip angle and perturbations of these phases of its force, yet the "variation " or, more properly, the Declina- tion of the magnetic needle has been chiefly studied by navigators and surveyors, as of immediate practical importance, and hence their records afford the most ancient data, and the best basis for magnetic investigations. When the intensity and dip have been fully correlated mathematically to the declination, we may be able to hope for a full knowledge of the general magnetic influence by means of observations of the declination alone. The declination of the magnetic needle is to us, therefore, the most important reaction of the magnetic force upon matter; and it i> for this reason, that I have specially studied, and made it the subject of the present paper. I here, therefore, present in tabular form:' (1.) A collection of observations of the magnetic declination at Albany, N. Y. (2.) A table showing prediction computations, which I have made by the mathematical formula hitherto regarded as the expression most conveniently representing the declination, according to the idea en- tertained by mathematicians, of the local magnetic law at Albany. The formula, by which the results in table second were computed, was devised by Prof. Charles A. Schott, chief of the computing division of the U. S. Coast and Geodetic Survey at Washington. This formula he calls empirical. It was prepared many years since on the basis of the few observations then available for this locality. The newly collected and observed data presented in this paper ex- tends more than one hundred years back of the data which Prof. Schott used as the basis of his formula; and, doubtless, on this new data a more exact formula may be constructed. Magnetic Observations. 7 I had hoped at this time to present a new formula of my own com- putation for this local magnetic law on the basis of the new data; but, as the time at my disposal has not been sufficient to permit me to as- sign weights (or estimates of precision) to each of the observations communicated, I must defer the pleasure of presenting this new formula until another time; and will merely transmit my observations and col- lated data, accompanied by computations by the old formula; which, while affording a scale of numerical comparison with the observations, will serve some present purposes, and give an idea of the supposed ex- tent of the secular change in declination and of the processes, so far, devised for the prediction of the phenomena. Using the old data only, the empirical formula of Schott for the magnetic declination at Albany is — D = + 8°-17 + 3°-02 Sin (1-44 m — 8°-3) in which D=the declination at any desired time in calendar years from the epoch 1850. From this formula it will be seen that the terrestrial magnetic force is not as simple a form of energy as gravitation; especially in view of the fact that this is only one expression, suited to only one locality, and not applicable to any even moderately distant place. This shows how important is the annual collection of local magnetic data, at a great number of points, if Ave are ever to attain a better understanding of the nature and origin of the magnetic force. The computations in table (2) by the old formula I have extended beyond the limits for Avhich they were probably intended in order to show the maximum and minimun points and numerical nature of the curve of declination according to Schott's formula, as well as to com- pare its values with the actual observations newly communicated in- the first table. In this table the last column shows the ± differences of the results by formula from the actual observations. With this explanation, this collection of data is herewith transmitted to the Institute, Avith the hope and intention that in a future paper these results will be discussed and some advancement made in the local theory and formula for the prediction of magnetic phenomena at Albany. TABLE I. Records of Observations of the Declination of the Magnetic Xecdle, at Albany, N. Y, beltoeen the years 1686 and 1892; collected and observed by Yerplanch Colvin. Note.—la 1609, September 13th, D = + 13° 00' was observed by Robert Juet, sailing-master of Hendrick Hudson's ship, the Half Moon, on tide- water of Upper Hudson. The year 1C80 was remarkable for five comets. In 1806 a remarkable total eclipse of the sun occurred, which General DeWitt thinks may have affected the earth's magnetism. Date. Month not given. Month not given. Month not given. Month not given. Month not given Probablv April . , July 30th....... September 4th.. . October 4th..... August 1st...... April 24th ..... September...... September...... September...... June........... May............ May............ November....... Declination. + 9° 09' North-west.. + 7 40 + 6 39 + 5 03* + 5 27 + 5 00 + 4 58 + 5 43 + 5 44 + 5 45 + 6 00 + 6 14 + 6 16 + 6 18 + 6 18 . + 6 25 + 6 32 + 6 40 • Remarks. Early record, Van Rensselaer patent. From notes of J. II. Bleeker, surveyor, etc. From notes of J. R. Bleeker, surveyor, etc. Records of Livingston manor. New York Documentary History. Prof. Joseph Henry. Simeon De Witt. Simeon De Witt. Surveyor-General of State of New York. Surveyer-General of State of New York. Surveyor-General of State of New York. State geological purvey. State geological survey. State geological survey. State geological survey. State geological survey. Geological survey. Regents' report and Silliman's Journal. * Corrected to Albany Station D = + 5° 34' November........... October............. October............. November........... August 31st......... September 1st....... May 12th and 14th.. . July 25th........... October 21st and 24th April 10th......... April 30th.......... April............... June............... June 3d........... May 22d............ June 5th............ June 28th........... April 25th.......... May............... July 19th........... February 3d......... November 22d....... 8 9 + 9 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 * Preserved on slips only; Regents' report and Silliman's Journal Silliman's Journal, 1838, vol. xxxiv. Silliman's Journal, 1838, vol. xxxiv. Regents' report. Prof. C. A. Schott. Karl Freisach, of Vienna. G. W. Dean, U. S. C. Survey. Verplanck Colvin, at station in grounds of his residence, between Western avenue and State street, Albany, N. Y. Latitude = 42 ° 39' 43" Longitude = 73° 46'33" " in time 4h 55ra 06s Altitude above sea level 227^%^^. TABLE II. Probable Mean Magnetic Declination at Albany, according to Prof. Schotts formula. [Empirical.] YEAR. January 1st, 1800............. 1801............. 1802............. 1803............. 1804............. 1805............. 1806............. 1807............. 1808............. 1809............. 1810............. 1811............. 1812............. 1813............. 1814............. 1815............. 1816............. 1817............. 1818............. 1819............. 1820............. 1821............. Computed Declination. + 5° 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 11'.5. 12 .6. 13 .6. 14 .7. 15 .7. 16 .8. 18 .4. 20 .0. 21 .6. 23 .2. 24 .7. 26 .9. 29 .0, 31 .1. 33 .2. 35 .3. 37 .9. 40 .5. 43 .1. 45 .7. 48 .3. 51 .4. 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