Vol. 6, 1920 
PHYSICS: C. BARUS 
495 
portion is to exceed the value for ordinary rockets, which is about Vs- 
This action consists in the loading and firing of a number of charges suc- 
cessively in the same combustion chamber. 
The results of work upon this feature, to date, have been the develop- 
tnent and experimental demonstration of a simple and light multiple 
charge apparatus, firing a few cartridges and travelling straight. In 
order to complete the development, it is necessary to adapt the apparatus 
to fire a large number of cartridges, and to make the parts, exclusive of 
propellant, sufficiently light. Work on increasing the number of cartridges 
is in progress. 
In order to complete the development with a minimum of expense, 
the perfecting of details should be carried out only insofar as is neces- 
sary in order to produce an inexpensive apparatus. The only expense of 
maintenance will be a new magazine for each ascent. 
In any case, the time required to reach the 10 km. level should be of the 
order of 20 seconds, if the retardation due to air resistance and gravity is 
minimized. 
As an illustration of what should be possible with an apparatus developed 
in this way, it may be said that, using as a basis for the estimate a velocity 
of ejection of 5,500 ft. /sec, which is easily obtained, a rocket weighing of 
the order of 11 lbs. initially and 6 lbs. at the highest point would be needed 
in order to send instruments weighing one pound to the 10 km. level. 
NOTE ON A PNEUMATIC METHOD OF MEASURING VARIA- 
TIONS OF THE ACCELERATION OF GRAVITY^ 
By Carl Barus 
Department of Physics, Brown University 
Communicated June 22, 1920 
1. Introductory. — Some years ago I made an extended series of experi- 
ments^ on the diffusion of gases through water; the gas in this work was 
imprisoned in a cartesian diver, and the very sensitive conditions under 
which the diver floats at a given level were made the criterion of measure- 
ment. 
Inasmuch as such experiments consist virtually of a comparison of 
weights with the forces derived from air pressures, it must, therefore, be 
possible to obtain the acceleration of gravity in terms of these pressures, 
just as in another place I shall describe interferometer experiments made 
to evaluate the changes of g in terms of torsion. It will not, of course, 
be possible to determine g absolutely in this way because so little air is 
used; but it was hoped that the changes of g, in a proper environment would 
be determinable with some precision. Quite apart from this specific 
purpose, however, the long range experimental data are of varied interest. 
