May 3, 1912] 
Cla’p 14(R—D) Mean 
No. Nights Residual 
Ez § —0".71+07.34—1"14sinzg +07.19 
W 2 —1"11+0".34—1”1lsing 407.15 
W 4 —1’.01-+ 0.83 —1’’.11 sin z == 07,15 
Ww 2 —1’.60 + 0’.40 —1”.11 sin 2 ss (0Cily/ 
W 2 —1" 48+ 0’.28—0”58sing +0”.16 
W 2 —1”.07 + 0.71 —1”.37 sing + 0”.18 
# 2 —0".81+07.22—0”.77sing +0/.28 
The agreement with the collimator measures is 
satisfactory. To test the cosine law, 20,000 star 
observations, corrected for division error, bisection 
error, variation of latitude and flexure, were dif- 
ferenced for successive clamp years. The mean 
values of (Si— Se) are: 
— 07.24, — 0.23, —0’.23, —0”.03, —0”.11. 
The residuals from these means were solved in the 
form 
0’.04 cos ge — 0”.11 cos 22. 
This reduced the mean residual from 0’.09 to 
0”.08, only, and has not been used. The mean dif- 
ferences (Si—Se) were attributed to the uncer- 
tainty in the various nadir division errors. The 
corrections, following, were, therefore, applied to 
the different years; their sum is zero: 
+0”.17, —0”.07, +-0’.16, —0”.07, —0’”.04, —0”.15. 
Tests with Standard Electric Lamps: E. S. Kine. 
These tests relate to two lamps, rated for 2- 
candle power, loaned from the Bureau of Stand- 
ards at Washington. In comparing these lamps 
with the Argand Standard, I have included 6 com- 
mercial lamps, which were regulated to approxi- 
mately the same intensity. The results for 8 com- 
parisons, made at intervals of about a day, show 
great constancy. The average deviation in magni- 
tudes for Lamp No. 1 is + 0.035, for Lamp No. 2 
= 0.031, for the mean of the 6 commercial lamps, 
= 0.030 and for the mean of all the lamps + 0.025. 
Comparisons with ten different stars were made 
by the out-of-focus method with the 11-inch Draper 
telescope on seven different nights. The resulting 
photographic magnitudes for the lamps at a dis- 
tance of 1 meter are as follows: Lamp No. 1, 
12.02; Lamp No. 2, 12.10; Lamp No. 8, 12.01. 
From the comparisons with the Argand the results 
are, Lamp No. 1, 12.05; Lamp No. 2, 12.12; 
Lamp No. 8, 12.04. These figures indicate that the 
lamps must be placed at a distance of about a 
kilometer to have the same photographie bright- 
ness as Polaris. 
Recent Interviews with Optical Glass Manufac- 
turers of France and Germany: J. A. BRASHEAR. 
Some Observations with the 60-inch Reflecting 
SCIENCE 
711 
Telescope of the Mt. Wilson Solar Observatory: 
E. E. BaRNnarp. 
Photographic Observations 
1911: HE. E. BARNARD. 
This comet when found by Brooks was a faint 
object without any tail. A long exposure photo- 
graph a few days after its discovery showed only 
a round diffused object with no signs of a tail. 
Later the comet developed a tail, and became 
visible to the naked eye and presented a splendid 
spectacle in the evening and then in the morning 
sky. Its naked eye visibility was of long duration, 
from August to December. 
Though it developed a slender tail early in its 
career it was very disappointing, for photographs 
made night after night did not show any changes 
worth mentioning and the comet promised to be of 
little interest from a photographic standpoint. 
The photographs on different nights simply re- 
peated themselves. In October, however, there was 
apparently a complete transformation of its nature 
and it really became one of the most interesting 
comets yet photographed. From the previous con- 
dition of a steady outflow of matter which marked 
its appearance until October the tail now presented 
a very active and remarkable appearance changing 
from day to day from one complex and beautiful 
form to another equally remarkable. The photo- 
graphic activity was also greatly increased, much 
more, apparently, than its inerease of light would 
account for. The phenomena of Morehouse’s 
comet were duplicated in almost every particular. 
This change in the nature of Brook’s comet did 
not seem to be due to any special change in its 
spectrum. Cyanogen did not appear at any time 
in the spectrum of the tail, though it was present 
in the head. This compound which was such a 
striking feature of the spectrum of the tail of 
Morehouse’s comet was supposed to be the cause 
of the remarkable phenomena of that comet. Its 
absence from the tail of Brook’s comet would seem 
to show that after all it was not necessarily the 
cause of the freakish nature of that comet. 
of Brook’s Comet 
Personal Equation Apparatus for Nine-inch 
Transit Circle, Naval Observatory: F. B. Lit- 
TELL. 
The new personal equation apparatus recently 
installed is based on the same principle as that 
devised by Professor John R. Eastman, U.S.N., 
but differs entirely in details and secures a much 
more exact reproduction of the circumstances of 
actual observation and more extended application. 
An artificial star moves alternately east and 
west across the line of sight at the focus of the 
