440 SCIENCE. 
In No. 15 the difficulty of determining 
permeability and hysteresis is pointed out, 
and it is shown that the pull in the perme- 
ater should be represented by 
S (B? — B-H)/8z instead of S (B® — H’)/8=. 
Mr. Wolff told the section of the present 
condition of the office of standard weights 
and measures at Washington, and the 
progress that has been made toward the 
equipment of the laboratory for the veri- 
fication of electrical apparatus. It is 
gratifying to know that even now we 
have a trustworthy bureau to which elec- 
trical standards may be sent for testing. 
He also presented some experiments as to 
whether current density affects resistance, 
that is as to the universal truth of Ohm’s 
law. If the resistance is expressed as a 
function of current density in the following 
form : 
ut ONE 
ahs | 1+ n(<) es is current den- 
sity, then A cannot be greater than 1/600,- 
000,000. 
In No. 20 were presented some extremely 
interesting and important generalizations 
with reference to the effect of broad areas 
of atmospheric pressure upon the weather. 
This paper will appear in The American 
Journal of Science. 
Mr. Brace in No. 21 and No. 22 presented 
some interesting optical matter whose ap- 
pearance in detail in the journals will be 
awaited with interest. 
Certainly one of the most important 
papers presented was No. 23, in which Mr. 
Fessenden presented a large mass of theoret- 
ical and experimental material tending to 
give a clue as to the nature of electricity 
and magnetism, and also to give a value 
for the elasticity and density of the ether. 
He pointed out the great advantage of dis- 
cussing physical problems by means of 
dimensional formule, showing that these 
were particularly valuable in pointing out 
[N. 8. Von. X. No. 248. 
the direction in which the investigation 
should tend, and in checking the results of 
more elaborate mathematical analysis. A 
detailed abstract of this paper is not em- 
bodied here, because it is believed that it 
will appear in ScreNcE before long. 
Everyone is now interested in the ques- 
tion of smokeless powder, and the freedom 
from observation which it gives to the 
soldier. It is interesting to see in this con- 
nection from No. 25, that Mr. Fessenden 
has discovered a very simple and appar- 
ently effective means of locating the flash 
from smokeless powder, by simply provid- 
ing the observer with a piece of pale red 
glass, it having been found that these flashes 
are strong in red light, whereas the general 
landscape is very weak in red. 
In No. 28 Mr. Fessenden raised the ques- 
tion as to whether it is necessary to sup- 
pose that the conditions of terrestrial radia- 
tion have always been similar to those 
which exist at present; in other words, 
as to whether Lord Kelvin’s estimate for 
the age of the earth which has been de- 
clared entirely inadequate by biologists, 
may not have to be extended, owing to an 
earlier excessive rate of radiation, due to 
the absence of a blanketing atmosphere. 
No. 29 and No. 30 are valuable contribu- 
tions to the subject of the wave-length of 
energy radiated from ‘black’ bodies at 
various temperatures. 
In No. 32 Mr. Cook has made some inter- 
esting computations as to the conditions of 
time and temperature necessary for a planet 
to lose an atmosphere consisting of gases, 
ranging in density from carbonic acid gas 
to hydrogen. 
No. 36 gives a continuation of Mr. Gray’s 
interesting investigation upon the dielectric 
strength of oils. He finds, for example, 
that the strength per cm. decreases as the 
layer increases in thickness. 
In No. 37 he has called attention to an 
error in a new Watt-meter, caused by the 
Fe ol Se 
— a - 7) 
