OctoseR 4, 1918] 
gravitation that we can explain further. It is 
the real definition of mass, and (3) is a useful 
additional postulate, or a useful experimental 
fact. 
So far as ease of thinking is concerned, 
which is more or less irrelevant, force and 
acceleration are far more easily grasped than 
mass. That is to say, it appears so to the 
writer; but Frederic Soddy* says: “the con- 
ception of force and its pseudo physical reality 
undoubtedly delayed for centuries the recog- 
nition of the law of the conservation of energy. 
Only what is conserved has the right to be 
considered a physical existence. In other 
branches of science, the conception is a stumb- 
ling block and a delusion.” Perrin takes a 
radically different view. There seems to be a 
certain mysticism in Soddy’s contention, for 
what do we care whether a force goes on 
“ existing ” when we finish with it? We find 
velocities and temperatures convenient, yet 
they go out of “existence” without any spe- 
cial regret. The main fact is we can give 
numbers to these forces, temperatures, etc., 
and make equations that correspond (some- 
what) to experiments. 
Mass, on the other hand, means (1) inertia. 
(2) capacity to be attracted by a gravitational 
field (3) capacity to create a gravitational 
field, and some other things. It appears to de- 
pend on velocity, though it is not intended to 
consider non-Newtonian mechanics. It is 
about as puzzling a thing as there is in physics 
—for who knows what gravitation is? 
Paut J. Fox 
1203 Stock EXCHANGE, 
PHILADELPHIA 
NONSILVERABLE CONTAINERS FOR SILVERING 
MIRRORS 
In the ordinary process of silvering glass 
mirrors by chemical decomposition (e. g., 
Brashear’s method) the metal is deposited 
upon the glass container. In this manner a 
great deal of silver which might have added 
to the thickness of the mirror is lost. This is 
an important item when silvering mirrors 25 
cm. or more in diameter. 
3‘‘Matter and Energy,’’ New York, 1912, p. 
108. 
SCIENCE 
345 
The object of this note is to call attention 
to the usefulness of ordinary, “ granite ware,” 
enamelled iron pans, which do not attract the 
silver and hence increase the supply of mate- 
rial available for deposition on the mirror. 
This was observed some years ago, but its im- 
portance was not very apparent. However, 
during the past year the writer has had fre- 
quent opportunities to verify this observation 
and to apply it in producing thick deposits of 
silver on glass. 
Wma. W. Cosientz 
BurEAU OF STANDARDS, 
September 9, 1918 
QUOTATIONS 
SCIENTIFIC WORK IN INDIA 
Tue Board of Scientific Advice for India 
has, like similar bodies elsewhere, felt the 
effect of war conditions. The board has been 
strengthened by the addition of a representa- 
tive of the Indian Munitions Board, and 
power has been conferred upon the president 
to appoint subcommittees, membership of 
which need not be confinel to members of the 
board, for the purpose of dealing with par- 
ticular investigations. The board has found 
it necessary to modify the treatment of pro- 
grams of work submitted by individual scien- 
tific departments, and to resolve that the an- 
nual report for 1916-17 be confined to a brief 
statement of work actually done during the 
year, also that the bibliography of publica- 
tions bearing on particular subjects be con- 
solidated. But the establishment of a Zoo- 
logical Survey recorded for the year under 
notice, has not affected the composition of the 
Board of Scientific Advice, representation of 
this subject having been provided for already. 
That its organization should have been so 
slightly affected affords striking evidence of 
the soundness of the original constitution of 
the board. i 
The report of the board for 1916-17 is an 
interesting document, and much of its con- 
tents, especially where the applications of sci- 
ence are concerned, may repay perusal out- 
side India. In agriculture the low values of 
