JANUARY 18, 1901.] 
sets firmly, apply this to the silver surface and 
allow it to harden. It should then be easy to 
remove the silver grating from the glass grating 
and the reproduction should have all the gloss 
and accuracy of the surface serving as the mat- 
vix. My interest in the matter was the possi- 
bility of easily and rapidly obtaining fairly good 
gratings without great expense, so that students 
in laboratories might use them without re- 
straint. From one good glass grating numer- 
ous reproductions could be had at any time. 
ELigu THOMSON. 
SwAMmescort, Mass., 
Jan. 5, 1901. 
THE FRICTIONAL EFFECI OF RAILWAY 
TRAINS ON THE AIR. 
AN interesting and in some respects excep- 
tionally important paper, read by Professor F. 
E. Nipher before the St. Louis Academy of 
Science has just been published by that Society 
in its transactions.* In this paper, the results 
of an experimental investigation of the effect of 
railway trains in the production of air-currents, 
and in causing the motion of adjacent bodies, 
are given with tabulated and diagrammed data. 
The effect of a rapidly moving express-train in 
producing strong air-currents is familiar to all 
who have seen anything of that kind of train- 
service, and the results of action of these fast- 
moving currents in overturning and in trans- 
porting objects near the track are hardly less 
familiar; but this is the first investigation con- 
ducted in a scientific and satisfactory manner 
to determine the quantitative measures of such 
effects. The stimulus to this particular re- 
search seems to have been the denial, by the 
Supreme Court of Missouri, that such effects 
are or can be produced.+ 
The station agents of all the great trunk-lines 
*The Frictional Effect of Railway Trains upon 
the Air; Francis E. Nipher. Trans. Acad. of Science 
of St. Louis; Vol. X., No. 10. Issued Nov. 12, 1900. 
{‘‘ When the case was tried a second time, and 
again resulted in a verdict against the company, the 
Supreme Court attacked the experts it had approved 
in the first reversal and threw out their uncontested 
evidence. * * * The Supreme Court of Missouri de- 
cides that the physical laws of the universe do not 
exist, so far as that august assemblage is concerned.”’ 
—St. Lowis Mirror, November 29, 1900. 
SCIENCE. 
115 
of railway over which fast trains are operated 
are invariably cautioned regarding this danger 
and are careful to warn people against standing 
near the track when an express train passes. 
Small articles, and especially bulky and light 
merchandise, may often be seen to move under 
the ‘suction’ so produced, and, in the case re- 
ferred to, a boy standing near the track, await- 
ing the passing of the coming fast train, and 
about to cross, was overthrown and rolled under 
the wheels and killed. The evidence showed 
that he was not struck by the train and the upper 
part of his body was not bruised. ‘ He fellafter 
part of the train had passed.’ The Court, how- 
ever, repudiated the evidence of two scientific 
men of recognized attainments and distinction, 
testifying to the existence of known facts and 
to the probability of the claim of the plaintiffs 
in the case. The outcome of this doubt of the 
evidence was the employment by Mr. Nipher of 
a large part of the succeeding summer in the 
investigations here recorded, which were carried 
on, on the various roads leading out of St. Louis 
to Burlington, Chicago and Cairo. The Illinois 
Central Railroad finally fitted up a special car 
for the work; this was employed in securing 
the larger part of the information published. 
The difference of pressure was taken between 
the interior of the car and some one point, se- 
lected by the observer, in making a series of 
observations from contact with the side of the 
car to a stratum several feet from the side, and 
the-successive differences of pressure consti- 
tute measures of the varying tendency to carry 
along loose bodies near the track and of the 
tendency, also, to rotate them. A cup-shaped 
collector was used and the Newtonian equa- 
tion was adopted. The coefficient, for pounds 
per square foot and miles per hour, was found to 
be 0.0025, very nearly, without wind. Still air is 
only reached at distances of sometimes many feet 
from the side of the train. The curve of vary- 
ing pressures relatively to the car was found to 
be, as plotted, approximately hyperbolic, the 
vertical asymptote finding its position a short 
distance inside the car. The pressures measured. 
range from 3.4 to 6 pounds on the square foot, 
at distances of 0 to 30 inches from the side of 
the car; the mean speed being 388 to 46, usually 
about 40, miles an hour; at which speed the 
