Du 
258 
numerous and valuable, and are sure of popular rec- 
ognition and reward; but they often come from the 
most unexpected quarters. No one can predict what 
wonderful points of contact may be suddenly revealed 
between a purely theoretical investigation and the 
practical utilities of life. Meanwhile, a deeper in- 
sight into the laws of the material universe, extorted 
from a reluctant nature only after long and patient 
labor and thought, and many disappointments, be- 
comes a permanent possession for mankind; and, 
as long as man does not live by bread alone, it is for 
him a perennial blessing. The academy, in award- 
ing the Rumford premium to you, has indicated the 
kind of scientific work which, in its opinion, tends 
most to promote the highest good of mankind. 
I ask you to accept, with these medals, my warm 
congratulations, and the cordial good wishes of all 
the members of the academy here assembled to 
administer Count Rumford’s trust. 
On receiving the medals, Professor RowLanp 
spoke as follows : — 
Mr. PRESIDENT, AND GENTLEMEN OF THE ACAD- 
EMY, I thank you for the honor you have conferred 
upon me, which I can but regard as the greatest 
honor of my life. 
In receiving these medals, I am pleased to think 
that they have been conferred upon work which is 
not the result of a happy accident, but of long and 
persistent endeavor. 
There are some investigators whose disposition 
permits them to follow their aim, inspired by the 
mere love of the labor and the work. There are 
others to whom the sunshine of appreciation is neces- 
sary. To either class, appreciation, when it comes, 
is always acceptable; and I assure you that the judg- 
ment set upon my investigations by this academy is 
highly valued by me. 
It has been intimated that a short account of my 
work would be of interest to the members of the 
academy. My attention was first called to the con- 
struction of dividing-engines by an inspection of a 
dividing-engine constructed by Prof. W. A. Rogers, at 
Waltham, in this state. On returning to Baltimore, 
I devoted much time to the general problem of such 
machines; and, through the liberality of the trustees 
of the Johns Hopkins university, I was enabled to 
construct an engine. In about a year this engine 
was finished. It worked perfectly the moment it was 
put together, and it has not been touched since. In 
order to rule diffraction-gratings, I reflected that it 
was necessary that the screw should be perfect, and 
that the rests for the plate which receives the ruling 
should also be as perfectly adjusted as is necessary 
in optical experiments. 
The process of making the screw consisted in 
grinding it ina long nut in which it was constantly 
reversed. When this screw was finished, there was 
not an error of half a wave-length, although the 
screw .was nine inches long. 
When the dividing-engine was completed, my mind 
was occupied with the problem of the best form of 
surface to receive the ruling. I speedily discovered, 
SCIENCE. 
[Vou. IIL, No. 56. 
a 
that, by ruling the lines on a concave mirror of 
long focus, I could dispense with a collimator and 
with the ordinary arrangement of lenses. I now rule 
gratings six inches long, with various numbers of 
lines to the inch. I find that there is no especial 
advantage in having more than fourteen thousand 
to the inch, with the ordinary conditions of ruling. 
Having made the concave grating, I invented a sim- 
ple arrangement for mounting it, so that a photo- 
graphic camera should move along the arc of a circle 
at one end of a diameter, upon the other end of 
which the grating was placed, and always remain in 
focus. With this apparatus, one can do in an hour 
what formerly took days. Moreover, the spectra ob- 
tained are always normal spectra, and every inch 
on a photograph represents a certain number of wave- 
lengths. 
After finishing my apparatus, I found it necessary 
to study photography; and I therefore devoted much 
time to this subject, and made a special study of all 
known emulsions. I discovered that an emulsion 
- containing eocene enabled me to photograph from 
the violet down to the D line; and other emulsions 
were used for the red rays. I have also been engaged 
in enlarging my negatives and in printing from these 
negatives. On these enlarged photographs lines are 
doubled which have always been supposed to be 
single. The E line is easily doubled. My map of 
wave-lengths is based upon Prof. Charles S. Peirce’s 
measurements of the wave-length of a line in the 
green portion of the spectrum. 
At the conclusion of Professor Rowland’s 
remarks, many questions were asked in regard 
to his beautiful device for photographing the 
spectrum, and the enlarged photographs which 
he showed were carefully examined. 
PROGRESS OF ELECTRICAL SCIENCE 
DURING 1883. 
THE subject of electrical science has become so 
broad that he who desires to keep abreast of the line 
of advance, and also to be on some points in advance 
of others, must read an immense amount in the Eng- 
lish, French, German, and Italian journals, and in. 
the patent-office reports of the various civilized na- 
tions. This is generally recognized; and courses in 
electrical engineering have been established in Eng- 
land, and are about to be established in America. 
This increase of intelligent appreciation of the mag- 
nitude of the subject of electricity is one of the fea- 
tures of the past year. 
Perhaps the most important text-book that has ap- 
peared during the year is the English translation of 
Mascart and Joubert’s treatise on electricity, with 
new notes by the authors. Clausius, also, has pub- — 
lished a treatise on the theory of the dynamo-electric 
machine; and there have been numerous articles in 
various magazines upon the general subject of math- 
ematical electricity. . 
The electrical congress which met in Paris, October, — 
