REPORT ON THE 
PHYSICAL LABORATORY 
OF THE 
MASS. INSTITUTE OF TECHNOLOGY. 
To Professor J. D. Runkle, President pro tempore of 
the Institute: — 
As the method of giving instruction in Physics by means of 
a laboratory is now attracting a good deal of attention both in 
this country and in Europe, it seems desirable to make known 
the success which has attended a laboratory of this kind lately 
established at the Institute. Its history is as follows : — 
1864. President Rogers1 proposed a laboratory in which 
“the student may be exercised in a variety of mechanical and 
physical processes and experiments.” 
1868, Oct. A room was opened to advanced students where 
they carried on physical investigations, as is done by many 
physicists, with their special students. 
1869, April. The plan described below was presented by 
the writer and adopted by the Government of the Institute.2 
1869, Oct. This plan was carried out, and the laboratory 
opened to the regular students of the Institute. 
1 Scope and Plan of the School of Industrial Science of the Mass. Institute of Tech- 
nology, p. 24. 
2 Supplement to the Fourth Annual Catalogue. Plan of the Physical Laboratory. 
8vo. Pamph., pp. 16. 2 
Its first object is to enable tbe regular students of the Insti- 
tute, after attending a course of lectures on Physics, to verify 
its laws and measure its constants, also to learn to use the more 
important pieces of apparatus. Secondly, to instruct special 
students in the use of particular instruments, or branches of 
physics, as the spectroscope, microscope, photometry, electrical 
measurements, etc. Thirdly, to prepare teachers of this science. 
And fourthly, to afford facilities to physicists to carry on inves- 
tigations at the Institute. 
In carrying out the first part of this plan the following diffi- 
culties presented themselves. How could experiments be 
performed by twenty or thirty students at a time, without 
duplicating apparatus to au extent which would involve a very 
great outlay, and how could each obtain sufficient attention 
from the instructor, to enable him to work with advantage? 
Moreover, since physical apparatus is often delicate and expen- 
sive, would not the injury and breakage, both in moving and 
using it, be so great as to render the current expenses of the 
laboratory very large ? It will be seen that these difficulties 
were obviated by the adoption of the following plan. Two ad- 
jacent rooms were fitted up with tables, and supplied with 
water and gas as in a chemical laboratory. On each table is 
placed the apparatus necessary for a single experiment together 
with a complete written description. Between the two rooms 
is an indicator, or frame with cards containing the names of‘ the 
experiments, and opposite each, a second card with the name 
of a student. Each member of the class on entering the 
rooms notices where his card is placed, goes to the proper table, 
reads the description, and sometimes is able to perform the ex- 
periment without any assistance from the instructor. The time 
of the latter is therefore sufficiently unoccupied to enable him 
to go from desk to desk, and watch carefully that no serious 
errors are committed. When an experiment is completed the 
card of the student is placed opposite some unoccupied table 
and he goes on as before. Since the number of experiments is 3 
greater than that of students, several places are always vacant, 
and delays are avoided. New experiments are added at in- 
tervals to replace those which have been performed. 
By this plan there is no need of duplicating apparatus, and 
since it always remains in the same place, the danger of break- 
age is very small; in fact, during the past year the loss in this 
way has amounted to almost nothing. It is, moreover, always 
ready for use, and so much time is saved in this way, that each 
student accomplishes a large amount of work. So much more, 
in fact, than was anticipated, as to cause during the past year 
some difficulty in supplying enough new experiments. The 
nature of the work done is best shown by the following 
examples. 
Deflection of Beams. I. A steel bar rests on two knife-edges 
and to it is attached a scale-pan on which are placed successively, 
100, 200, 300 to 1900 grammes, and the flexure measured by a mi- 
crometer screw, reading to °f an inch. The point of contact is 
determined with the utmost precision by connecting micrometer and 
bar with a galvanic battery and galvanometer, in such a way that the 
current only passes when the two former are in contact. The screw 
is turned until the needle moves, and the reading is then taken. The 
results are represented by a curve, in which horizontal distances cor- 
respond to weights, and vertical to deflections. This should give a 
straight line, and in many cases the difference is so small as to be 
scarcely perceptible to the eye. The experiment is then repeated, 
keeping the weight constant in amount, but altering its position. By 
moving knife-edges, micrometer or weight, and changing the magni- 
tude of the latter, this experiment may be infinitely varied. 
Deflection of Beams. II. A mirror is attached to the end of a 
beam, and the image of a scale is viewed in a telescope placed oppo- 
site it; a method of very general application for measuring small 
changes of position. 
Hook's Joint. A model of Oldham’s modification of this form of 
universal joint, has a graduated circle attached to each axle. Ohe is 
made to vary uniformly 5° at a time, and the difference in position of 
the two wheels is recorded. The result is represented by a curve, in 
which horizontal distances represent the position of the first wheel, 
and vertical the difference in the two readings. The values given by 
the formula tang a = cos A tang b, are then computed, and the theo- 
retical curve constructed on the same sheet of paper. 
Law of Lenses. The image of a gas flame is projected on a screen 
by means of a lens, and the latter is moved half a foot at a time. 4 
The image is focussed by moving the screen, and the positions of the 
latter are compared with the theory by means of two curves, as in 
the preceding experiment. 
Spherometer. The radius of curvature of each surface of two 
lenses is measured, and their foci computed. 
Hydrometers. The specific gravity of several liquids is measured 
by these instruments, also of a solid by Nicholson’s hydrometer. 
Gauge Flask. The specific gravity of a liquid and solid is meas- 
ured in this way also. 
Mohr's Balance. The specific gravity of similar substances meas- 
ured a third time by the hydrostatic balance. 
Specific Heat. The specific heat of a stone measured by the 
calorimeter, first testing the method by water. 
Opthalmoscope. A model of the eye intended for use with this 
instrument has been procured, together with representations of the 
principal diseases of the retina, and means of imitating near or far- 
sightedness and astigmatism. The student views the retina under 
these various conditions, using both the direct and the inverted image, 
and finally a diseased retina is inserted, and he is required to draw it 
as seen with the opthalmoscope. 
Spectroscope. The principal lines of the solar spectrum, also those 
of the spectra of soda, lithium, baryta, strontia and lime, are measured 
and drawn. Three mixtures of these substances are then given to 
the pupil, which he is required to analyze. 
Microscope. I. With this instrument the student views various 
objects, one being selected to show the effect of a diaphragm, another 
for oblique illumination, a third for reflected light, etc. 
Microscope. II. With a more complex microscope he makes 
drawings with a camera lucida, uses a lieberkuhn, and measures 
various distances with stage and eye-piece micrometers. 
Polariscope. A simple form of polariscope with a piece of com- 
mon glass for a polarizer is used with plates of selenite, crystals and 
compressed and unannealed glass. 
Cross Hairs. This experiment consists in the insertion of cross 
hairs in the eye-piece of a common telescope or microscope. It is 
done by unravelling a common silk thread, and stretching two fila- 
ments at right angles to each other on a circle of card-board, which 
is then fastened to the diaphragm of the eye-piece. Considerable 
tension is needed to render them straight, and as they are nearly as 
fine as a spider’s web the student acquires a good deal of delicacy of 
touch in handling them. 
Cathetometer. This instrument is placed opposite a bent tube in 
which a short column of mercury balances a long column of water. 
Their lengths are measured, and from this the specific gravity of the 
mercury is deduced. A barometer tube is next filled and its height 
measured, deducing the level of the mercury by the usual method 
with a pointed steel rod. The result is finally compared with a 
standard barometer. 5 
The above are some of the most successful experiments we 
have used, of which the whole number exceeds forty, and will 
probably be nearly doubled during the coming year. In select- 
ing experiments, care is taken to introduce some which shall 
illustrate general methods of research, such as the micrometer 
screw, verniers, interpolation, computation of probable errors, 
etc. The graphical method is very largely used, both from its 
value in studying laws, and from the facility it affords for 
determining the accuracy of the results. As stated above, 
when practicable, two curves are drawn on the same sheet; 
one obtained by experiment, the other by computation. The 
student has thus the most convincing proof of the correctness 
of his theory. 
The scale on which this laboratory has been tried, is such as 
to render its success no longer a matter of conjecture. In 
October last, the Third Year’s Class, numbering twenty-three 
students, were admitted into it, and have since then had thirty- 
six exercises of one hour each. In March, the Second Year’s 
Class, of twenty-four students, entered it, and have had twelve 
exercises. The total number, including special students, 
amounts to nearly sixty. The Third Class performed about 
four hundred experiments, the Second Class two hundred; 
the greater relative number of the latter being mainly due to 
the fact that the apparatus was in more perfect working order 
after being used for some months. Most of the experiments 
described above occupy but one hour, although such as the 
microscope and spectroscope require a longer time. Accord- 
ingly, an average student could perform all the experiments of 
the above series in less than thirty exercises of one hour each, 
and would thus acquire a far more practical knowledge of 
physics than by devoting the same time to lectures. Since the 
regular course of manipulations at the Institute is more than 
double this number, it is believed that each student will acquire 
as extended a knowledge of practical physics as is needed for 
everyday life. 
The degree of accuracy attained in these experiments is 6 
much greater than was anticipated, and led to the belief that 
investigations could be carried on, in which most of the exper- 
imental portion should be done by students. Such work would 
be of the utmost value to them, since, while learning to use the 
apparatus, they would he initiated into the methods of con- 
ducting researches, while the results being obtained by several 
independent observers, would be free from personal errors. 
To test this plan, experiments were made to determine the 
degree of accuracy attainable with the hook gauge, the cal- 
ibration of gas meters, the perfection of compensation of the 
so-called “ cycloid” of gas holders, and various other questions. 
The results will be published elsewhere, and are so encourag- 
ing that this method will be greatly extended during the com- 
ing year. 
Students in the higher classes who wish to pursue Physics 
further, after finishing the above course, perform more difficult 
experiments, and carry on original investigations. As an ex- 
ample of the work thus accomplished, see an article by Mr. 
Chas. R. Cross, On the Focal Length of Microscope Objectives, 
in the Journal of the Franklin Institute, for June, 1870. 
When a student wishes to pursue a special branch of physics, 
or to study a single instrument, the course is arranged to suit 
the requirements of each case. For example, a student, wish- 
ing to learn to use the spectroscope, would first perform the 
experiments of the general course bearing on this subject, such 
as measurement of the angles of prisms, of the power of tel- 
escopes, insertion of cross-hairs, determination of the index 
of refraction of different, rays, and the wave lengths of the 
more prominent lines of the spectrum. lie would also use the 
spectroscope, as described above, only with a greater variety of 
substances. After attaining some proficiency with this instru- 
ment, in which measurements are made with a photographed 
scale, a second spectroscope with graduated circle is given 
him, and with it he measures as before, the principal lines of 
the solar spectrum. He then constructs a curve, in which 
vertical distances represent scale-readings and horizontal wave- 7 
lengths, and thus has a means of reducing all his measurements 
to the normal spectrum. This method is then applied to elec- 
tric spectra, obtained by a Ruhmkorff coil. The lines of gases 
are obtained by Gessler tubes, those of metals bv using them 
as terminals, also by drawing the spark from the surface of so- 
lutions of their salts. These measurements are reduced to 
wave lengths by the curve, and platted as before. In this ex- 
periment he learns to prepare a battery, and to use the induc- 
tion coil. Next, he uses the large spectroscope belonging to 
the Institute (which produces a dispersion equal to eleven 
prisms of 60°), and with this he compares parts of the solar 
spectrum with Angstrom’s chart, new lines being measured by 
the spider line micrometer, and interpolated from those on the 
map. He also reverses spectra and projects images on the slit 
with this instrument. The projection of the solar and metallic 
spectra on a screen and the spectrum-microscope will be added 
hereafter, and eventually the means of observing astronomical 
spectra, especially those of the solar protuberances. This ex- 
ample is selected since it has been performed substantially, as 
here described, by a student in spectroscopy. 
Although the large number of colleges springing up all over 
the country has caused quite a demand for physicists, yet here- 
tofore there has been no place where a young man could be 
specially educated for this profession, and consequently instruct- 
ors have, in many cases, been selected from those who pre- 
viously have devoted but little attention to this subject. To 
teach physics properly it is necessary that the instructor, be- 
sides possessing a knowledge of its phenomena and laws, 
which can be obtained from text-books and lectures, should 
be a skillful experimenter; and he should be able to construct, 
or at least superintend the construction of apparatus, since 
most institutions are unable to afford to purchase large quan- 
tities of that already made. If, as is usually the case, the 
instruction is given by lectures, he must be able to speak 
fluently, and to perform difficult experiments in the presence 
of an audience. 8 
This course, therefore, in addition to the lectures and ma- 
nipulations described above, will offer an opportunity to the 
student to perform all the more common lecture room experi- 
ments, and especially the projection of photographs and other 
objects on the screen, using the electric and other lights. Af- 
ter each lecture given to the regular students of the Institute, 
he will be expected to repeat all the experiments there tried. 
Special instruction. will be given in designing apparatus and 
preparing estimates of its cost. It so often happens that a 
physicist is dependent on his own resources for most of his 
apparatus that students will he urged to make various instru- 
ments themselves, and will he shown how gas and steam fittings 
may be used, and how much may he accomplished by the aid 
of the carpenter and tinman. 
To give him ease in addressing an audience, exercises will be 
held in which each student in turn will present essays on vari- 
ous physical subjects illustrated by experiments, care being 
taken to select such as will be of value to all members of the 
class. 
The fourth object of the laboratory is to supply a place 
where investigations of a high order can be carried on. A 
physicist can here have water, gas, steam, and apparatus of all 
kinds, which could elsewdiere be obtained only at great expense. 
The large size of one of our room's (nearly an hundred feet in 
length) enables many experiments to be tried on a much larger 
scale than is usually practicable, while assistants can be ob- 
tained from among the more advanced pupils of the laboratory 
with mutual advantage to both parties. 
In conclusion, it seems scarcely necessary to point out the 
advantages of the laboratory system of teaching physics, since 
the tendency of all technical education is now in this direction. 
In Chemistry, especially, this method has proved so successful 
as to have almost superseded instruction by lectures, at least in 
the larger schools and colleges. 
Respectfully submitted, 
* Edward C. Pickering, 
Thayer Professor of Physics.