87 
PART I. 
RESULTS. 
(1) Origin and Purpose of the Experiments. 
The development of depth charges and non-contact mines as a means of 
destroying submarines has made it necessary to investigate as fully as possible the 
effects of different charges under water, at different distances, and under different 
conditions of depth, &c. The damage inflicted by a non-contact charge is due to a 
pressure wave transmitted through the water, and it is the law of action of this 
pressure wave that requires investigation. 
The most fundamental way of attacking the problem is to make an exact physical 
study of the pressure wave springing from different charges, and then, as a second 
step, to determine the relation between the physical constants of the pressure wave 
and its damaging power. 
This has been a recognised aim of investigation since observation mines were 
introduced in the American Civil War, and in fact the most extensive experiments on 
the subject, up to the present, were those made between 40 and 50 years ago by 
Lieut.-Col. H. L. Abbot, U.S. Engineers (“xperiments to develop a system of 
submarine mines, &c.’”—No. 23 of the professional papers of the Corps of Engineers 
of U.S. Army). Abbot's work, however, suffered from the limitation that the only 
quantity which he attempted to measure was the intensity of the pressure at different 
points in the water; there were no means for determining the duration of the 
pressure or the character of its rise and fall, though these are factors which may be of 
equal importance as regards the effect on a ship. The same remark applies to the 
continuation of Abbot’s work in recent years by Lieut. Schuyler, U.S.N. Moreover, 
present knowledge shows that, even as regards maximum pressure, the gauges used 
by Abbot and Schuyler were too sluggish to give correct results (Section 19). 
The necessity for fuller investigation, taking account of time as well as pressure, 
was urged on the Board of Invention and Research in 1917 by Sir R. Threlfall, and at 
his instance an attempt was made by the writer to develop gauges that wonld give 
more complete information. In the first half of 1918 a successful system of gauges 
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