OCTOBER 29, 1897. ] 
PHYSICS AT THE DETROIT MEETING OF 
THE AMERICAN ASSOCIATION FOR THE 
ADVANCEMENT OF SCIENCE. 
Section B of the American Association for 
the Advancement of Science met with Profes- 
sor Carl Barus in the chair and Professor 
Frederick Bedell as Secretary. ‘ Long Range 
Temperature and Pressure Variables in 
Physics’ was the subject of Professor Barus’s 
vice-presidential address, which has been 
published in fullin Scrzencr. It was very in- 
teresting ana was very well received. The 
address dealt with the historical develop- 
ment of pyrometry and piezometry, with a 
view to the present state of progress in 
these subjects, and with especial reference 
to their application to problems on the 
physics of the earth’s crust. 
The first paper on the list was by Pro- 
fessor F. P. Whitman and Miss Mary C. 
Noyes on the effect of heat on the elastic 
limit of copper wire. Their work was a 
continuation of a research on the effect of 
heat on Young’s modulus (published in 
the Physical Review, Vol. II., p. 277). The 
yield-point was found to increase as the 
wires were stretched, heated and cooled. 
From a long series of tests made on the 
same wire it appeared that the wire was 
approaching a permanent condition. If 
the wire was heated to a red heat, or if it 
was stretched considerably beyond its elas- 
tic limit at the start, it maintained a nearly 
constant state afterwards. There were 
curves shown which graphically represented 
the changes in the behavior of the wire. 
Professor A. Li. Foley next read a paper 
on ‘Arc Spectra.’ He examined the light 
coming from the are and found that it was 
due to concentric layers of different color. 
He used a concave grating to throw 
the spectra of different parts of the arc 
upon photographic plates. The outer layer 
was found to be strongest in the yellow. 
The upper carbon, whether positive or nega- 
tive, was covered toa greater depth with 
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649 
the yellow flame. Inside the yellow was a 
blue area stronger at the positive carbon, 
and inside the blue and at the positive car- 
bon violet was found. 
Mr. Chas. F. Brush read a notable paper 
on the transmission of radiant heat by gases 
at varying pressures. Before describing his 
own investigations he referred briefly to 
those of Dulong and Petit, who used a 
large copper ‘balloon,’ about three deci- 
meters in diameter, coated with lamp-black 
on the inside, in the center of which the 
thermometer bulb was placed. In discuss- 
ing the cooling of bodies in vacuo Dulong 
and Petit fell into the grave error of deduc- 
ing the behavior of the last few millimeters 
of gas from that of the rest. In this way 
they arrived at their ‘Sixth Law:’ The 
cooling power of a fluid diminishes in a 
geometrical progression when its tension 
itself diminishes in a geometrical progres- 
sion. If the ratio of this second progres- 
sion is 2, that of the first is 1.366 for air, 
etc. Mr. Brush said that his own obser- 
vations show that this law can be ap- 
proximately true only in the case of a 
large balloon, and at pressures from a few 
millimeters upward; that there is no sug- 
gestion of it where a small balloon is 
used, and at small pressures it does not 
obtain with either large or small bal- 
loons; he found that in a small balloon the 
cooling effect of the last millimeter of air 
is nearly ten times as great as that of all 
the rest, up to atmospheric pressure, com- 
bined. It was through misplaced confi- 
dence that Dulong and Petit were led to 
place a value on the rate of cooling in 
vacuo, something like a hundred per cent. 
too high ; and as they derived the cooling 
values of gases by deducting the cooling 
effect of a vacuum from the total, all their 
values for gases are much too low. This 
error vitiates much of their other work. 
Mr. Brush carried his observations down to 
those made at one-twentieth of a millionth 
