414. A. M. Mayer—New form of Lantern-Galvanometer, 
(“Remarks on uniformity of nomenclature in regard to micro- 
scopical objectives and oculars,” American Naturalist, March, 
1872, p. 136). This paper contains much valuable matter, and 
should be read by all who are interested in this subject. I learn 
from it for the first time that the method of determining the 
magnifying power of objectives by removing the field glass of 
the eye-piece and using eye-piece and stage micrometer as de- 
scribed above, has already loot used by Dr. J. J. Higgins of 
New York (American Naturalist, Dec., 1870, p. 628), to whom] 
asten to give the credit due. 
I am very glad to find Dr. Ward indicates the feasibility of 
the substitution of magnifying powers at a fixed distance as 
names for objectives instead of alleged equivalent focal lengths 
must, however, differ from him when he recommends thatthe 
Dr. Ward’s paper also contains some interesting suggestions 
on the subject of the nomenclature of eye-pieces, a matter which 
will, however, I think, particularly in the case of the ordinary 
eye-piece, require further discussion. I agree fully with Doctor 
rately measured? To this subject I may recur at some future 
time. 
— 
FRED M. Mayer, Ph.D., Professor of Physics 
Stevens Institute of Technology, Hoboken, N. J. 
Art. LIUL— On a new form of Lantern -Galvanometer a iy 
On the 21st of December, 1871, I delivered a lecture 7 
Magnetism before the American Institute, at the Academy pei 
Music, in the city of New York. It was necessary for 19 
$ etism 
experimental discussion I then made of the earth's magn of 
to use a galvanometer, so constructed that the least deflection 
its needle would be visible to a very large audience; at 8 
same time the astatic condition of this needle had to 
pe 2 
