509 
- 2B. 
The values of & in the p/t record of an explosion, after reduction to standard circuit conditions 
(C = .01 mfd. V = 3000 volts), can at once be plotted in terms of pressure when the constant of the gauge 
is known. 
5. Lay-out of Charge and Gauges in the Sea. 
when firing large charges of the nature with which we are concerned in this report, the place 
chosen for the experiment must be at a considerable distance from the shore and in reasonably deep water. 
A point of vital Importance is the distance of the gauges from the charge, whilst a secondary, though not 
unimportant, point retates to the depth of the charge and the gauges betow the surface and their distance 
from the sea-bed, The majority of the charges fired in this investigation were situated at a point in 
the 'prohibited area’ off Ryde, Isle of Wight - the depth of water being approximately 17 fathoms. For 
the purpose of the large-scale experiments two vessels are required, on one of which ('Carstairs' and later 
'M.22") is installed the oscillograph recording apparatus and accessories. The second vessel (‘Skylark* 
or 'Redwing') lays the 'trot', i.e, the system of buoys, wire, gauges and charge, as it gradually drifts 
away from the first vessel (at anchor), a stee) hauser and a grass line ccnnecting the two vessels. It 
should be mentioned at this puint that in the large-scale trials the p.e. gauge was only one of a large 
number af other gauges (these being essentially mechanical in character) laid at the same time. A series 
of bucys attached at definite points of the steel cable connecting the two ships suppert the weight of 
the charge and a number of steel girder-section frames which carry the gauges. Supperting wires, which 
suspend these frames from the main steel trot-wire, are cut tc definite lengths thereby locating the 
frames (and consequently the gauges which they carry. with respect to the charge, At the moment of 
firing the charge the second vessel starts her engines and pulls on the trot-wire. In this manner the 
trot is straightened out and uhe frames hang at their scheduled distances from the charge. with this 
arrangement of heavy frames and measured lengths of wire it is not possible that errors of distance due 
to tidal action on the frames can be of serious importance. The distances are considered accurate within 
+ 1 foot. 
Large scale experiments were only carried out when the sea was moderately calm. 
{n addition to the above mentioned large scale trials, however, a considerable number of small 
charges (24 lbs. and 18+ lbs. G.C.) were fired for other purposes. with these smaller shots the second 
vessel was unnecessary, all gauges etc. being laid from the first ship (e.g. M-22) at anchor, the tension 
on the trot-wire being maintained by a small boat or by 4 large buoy. (It should be observed that in 
these cases the heavy iron girder frames were not used and the gear on the trot was comparatively light. 
Extra precautions (additional wires, etc.) were taken to ensure that the charge-gauge distancee were 
correct. Particular attention was also paid to the method of slinging the p.e. gauges to ensure that 
they were oriented in a definite direction with respect to the line of the charge, and that they were 
situated at an appreciable distance from resonant meta? bodies (other gauges or frames) and from air 
cavities (e.g. diaphragm gauges). 
In certain cases, e.g. where it was desired to record surface or bottom reflections of the explosion 
pulse, the gauge and charge were necessarily suspended on Jong wires. In such circumstances the spread of 
the 'v' to the two supporting buoys was very smal). in these cases the charge was fired at slack water to 
ensure the gauge and charge hanging vertically and at the correct depths and distances apart. Reference 
will be made later to certain observations of the velocity of the explosion wave. In these experiments 
the two p.e. gauges used were bolted at a definite distance apart (known to .05 inches) on a 6 feet iron 
girder, the charge and pressure switch being arranged about 10 feet away on an extension of the line of 
the girder. 
Occasional large charges (300 1b. H.11 mines or depth charges) were fired in connection with 
other work of Vernon M, and in some of these cases it was possible also to obtain p.e. records. In these 
circumstances it was not always convenient to employ the usual trot arrangement to ensure accuracy of 
distance, and less accurate methods were adopted. 
In general, however, the distances in the experiments were known, as stated above within + 1 foot. 
Gecenes 
