PHYSICS: WEBSTER AND THOMPSON 259 
Lewis has already pointed out that a theory of the kind outhned in this 
paper explains satisfactorily the facts which have led many chemists to assume 
polar valence. For example, the chlorine atom in chlor-acetic acid, because 
of the relatively large charge on its kernel, as compared for example with a 
carbon atom, tends to displace towards itself the electrons holding it to the 
carbon atom. This effect is transmitted with gradually decreasing intensity, 
to the further end of the molecule, where it results in drawing the pair of 
electrons which holds the hydrogen nucleus to the octet of the oxygen atom, 
away from the hydrogen nucleus. Another way of looking at the effect is to 
consider that the positive kernel of the oxygen atom is displaced toward the 
hydrogen nucleus, and thus tends to weaken the force holding it. This 
effect makes it easier for the hydrogen nucleus to separate from the rest of 
the molecule as a positive ion. It is felt that this explanation can be applied 
in general to explain nearly all cases where polar valence bonds have been 
assumed in the past. This question will be discussed in more detail in the 
second paper to be published in the Journal of the American Chemical Society. 
1 Lewis, G. N., /. Amer. Chem. Soc, 38, 1916, (762-785). 
2 This will be published in full in a paper soon to be submitted to the Journal of the Amer- 
ican Chemical Society. This second paper will deal in some detail with the application of the 
Octet Theory to organic chemistry, particularly to nitrogen, sulphur, compounds, etc. The 
stereoisomerism of such compounds will be discussed. 
A NEW INSTRUMENT FOR MEASURING PRESSURES IN A GUN 
By a. G. Webster and L. T. E. Thompson 
Ballistic Institute, Clark University, Worcester, Massachusetts* 
Read before the Academy, April 29, 1919 
It is now over fifty years since the crusher gauge was invented for measur- 
ing the maximum pressure developed in a gun. This apparatus has probably 
gone through iewer changes than almost any physical instrument except the 
telegraphic sounder. It is looked upon by all experts as inaccurate, and 
should be superseded. We have developed an apparatus which shows not 
only maximum pressure, but also the pressure at any time while the projectile 
is in the barrel; that is, it gives the curve which represents the pressure as a 
function of the time. Attention is called to the fact that this curve is not ob- 
tained by a series of points, and that no part of the curve is missing. The 
success of this instrument is due to its being designed in accordance with the 
principles of dynamics, and of optics. 
The general nature of the apparatus is shown in figures 1 and 2. The 
success of such an apparatus that is to be free from vibrations of its own 
is brought about by using an extremely stiff spring. Such a spring is 
obtained by a short, steel girder, or a circular plate, the girder being shown in 
* Contribution from the Ballistic Institute, Clark University No. 4. 
