650 
of an atmosphere and found that the rate of 
cooling did not break down materially even 
then. To measure pressures he constructed 
two McLeod gauges. These gauges and their 
use Mr. Brush described in another paper 
on the measurements of small gaseous 
pressures. He gave, as an example of the 
delicacy with which small pressures were 
measured, the measurement of about two 
millionths of atmospheric pressure, with a 
probable error of only one part in three 
thousand of the quantity measured. From 
this he concluded that, with the apparatus 
described, small gaseous pressures might 
be easily measured with a probable error of 
less than a thousandth part of the millionth 
ofan atmosphere. Mr. Brush showed many 
figures and curves to illustrate his work. 
Professor W. A. Rogers read a paper on 
a final determination of the relative lengths 
of the imperial yard of Great Britain and 
the meter of the archives. 
Professor Nicholsread Mr. §. G. Barnett’s 
paper on the influence of time and tempera- 
ture upon the absolute rigidity of quartz 
fibres. Mr. Barnett found no time effect 
even after three months and an exceedingly 
small positive temperature coefficient of 
about three ten-millionths. 
The discharge of electrified bodies by X- 
rays, by Dr. C. D. Child, was a subject 
which has been interesting scientific circles 
of late. The air, and in fact almost every 
gas, isan excellent insulator under ordinary 
conditions; but when acted upon by X- 
rays it becomes for the time a conductor. 
The resistance offered to the passage of elec- 
tricity under these circumstances depends 
upon the pressure, temperature and kind 
of gas, as well as upon other more obscure 
causes. Dr. Child’s paper deals especially 
with the influence of the pressure of the gas. 
He finds that, when the pressure of the air 
is increased from a few millimeters of mer- 
cury up to atmospheric pressure, the rate 
at which electricity can be conducted by 
SCIENCE. 
[N. 5. Vou. VI. No. 148. 
the air in general increases to a maximum 
and then decreases again. The pressure at 
which the conductivity of the air is greatest 
depends upon the HE. M. F. tending to send 
current through it. If the H. M. F. is high 
the pressure for maximum conductivity 
seems to be greatly in excess of atmospheric 
pressure and lies beyond the range of Dr. 
Child’s measurements. 
In addition to a careful study of the effect 
of pressure upon the phenomena, Dr. 
Child has also investigated several other 
points, some of which have heretofore been 
in dispute. For instance, he finds that 
electricity can be continuously discharged 
from a charged body under the influence of 
X-rays, even when the body is covered 
with a solid insulator, such as a thin layer 
of paraffin. This result agrees with the 
observations of Professor J. J. Thomson 
and contradicts in part the conclusions of 
Lord Kelvin. Dr. Child has also studied 
the effect of X-rays developed by an induc- 
tion coil when the rate of interruption is 
varied. Many parts of Dr. Child’s work 
which cannot even be referred to here will 
go far toward explaining the irregular and 
contradictory results which most observers 
in this line have heretofore obtained. 
Professor F. P. Whitman described some 
investigations which he had made on the 
brightness of pigmented surfaces under 
various sources of illumination. The colors 
of the surfaces were ten in number, rang- 
ing through the spectrum. ‘The flicker 
photometer was used for the comparisons, 
and some very interesting information was 
obtained. 
Professor H. 8. Carhart read a paper on 
the design, construction and test of a 1,250 
watt transformer which had been made un- 
der his directions by two of his students. 
The core type was chosen instead of the 
shell, for reasons of convenience, as the iron 
for the core could be cut at the tinsmith’s 
without a die. From the data obtained in 
