38 THE VOYAGE OF H.M.S. CHALLENGER. 



probably due to a species of hydraulic-ram behaviour on the part of one of the valves of the pump. 

 These are little conical pieces of steel, with the points much elongated, which are ground accurately 

 into conical beds, and fall back into their places by gravity. It was not observed that this powerful 

 vibration had in the least degree altered the position of the indices in the thermometers or gauges 

 which were in the pressure-chamber. Their indications agreed perfectly with those of the preceding 

 and succeeding day. 



I made a number of experiments with the view of determining the amount of distortion at which 

 glass gives way, with the view of finding the limit of strength of a glass tube, and also the ratio of 

 external to internal diameter to secure it against any assigned lower pressure. 



The approximate results of these experiments is given in Appendix A, but I allude to them now 

 in consequence of a curious fact observed, which gives the explanation of a singular occurrence noticed 

 on board the Challenger. The walls of the tubes, when they gave way, were crushed into fine 

 powder, which gave a milky appearance to the water in the compression apparatus. But the frag- 

 ments of the ends were larger, and gave much annoyance by preventing the valves of the apparatus 

 from closing. To remedy this inconvenience, I enclosed the glass tube in a tube of stout brass, closed 

 at the bottom only, but was surprised to find that it was crushed almost flat on the first trial. This 

 was evidently due to the fact that water is compressible, and therefore the relaxation of pressure 

 (produced by the breaking of the glass tube) takes time to travel from the inside to the outside of 

 the brass tube ; so that for about xuooo^ 1 °^ a sec ond that tube was exposed to a pressure of four or 

 five tons weight per square inch on its outer surface, and no pressure on the inner. Tbe impulsive 

 pressure on the bottom of the tube projected it upwards, so that it stuck in the tallow which fills tbe 

 hollow of the steel-plug. Even a piece of gun-barrel, which I substituted for the brass tube, was 

 cracked, and an iron disc, tightly screwed into the bottom of it to close it, was blown in. I have 

 since used a portion of a thicker gun-barrel, and have had the end welded in. But I feel sure that 

 an impulsive pressure of ten or twelve tons weight would seriously damage even this. These remarks 

 seem to be of some interest on several grounds, for they not only explain the crushing of the open 

 copper cases of those of the Challenger thermometers which gave way at the bottom of the sea, but 

 they also give a hint explanatory of the very remarkable effects of dynamite and other explosives 

 when fired in the open air. [It is easy to see that, ceteris paribus, the effects of this impulsive pressure 

 will be greater in a large apparatus than in a small one]. 



Appendix E. — Tabular Synopsis of the General Results of Experiment and Calculation. 



The first four columns of the table give the numbers by which the various thermometers were 

 distinguished ; 1 in my Laboratory, 2 on board the Challenger, 3 by Captain Davis, 4 by the maker 

 Mr Casella. 



The series of thermometers A 1, ... . A26, though they were used on board the Challenger, are 

 the private property of Sir Wyville Thomson, and were not uniformly stamped, as were the Challenger 

 thermometers proper, with their numbers on the copper cases. Hence, when they were obtained from 

 Captain Tizard, it appeared necessary to put on some distinguishing mark, and the titles X, LV, + , &c. 

 were the chance devices on little tablets which were at once affixed to each of the instruments which 

 had no outward distinguishing mark. I have since found the means of recognising, without uncer- 

 tainty, each of the instruments. 



