414 



NATURE 



{March 6, 1879 



into the lake in its lower part when it is covered with ice, 

 must supply water at 32° F ; for even if it were at a higher 

 temperature while forming part of the stream, it would, 

 by impinging on the edge of the lake ice, be cooled down 

 before being able to mix with its waters. It would thus 

 (enter the lake at 32° and would spread itself out imme- 

 diately under the ice, and its effect on the temperature of 

 the water would be similar to that produced by the thick- 

 ening of the ice and conduction from it. 



The excess of water which falls into the upper and 

 open part of the lake must also find its way under the ice 

 to the outlet. In order to estimate its effect, we must 

 consider the conditions obtaining at the terminal edge of the 

 ice stretching across the lake. We have already discussed 

 what takes place when the first ice fringe forms at the 

 sides of a lake, and we may look on the ice covering the 

 lower and shallower part of the lake, as the fringe on that 

 side of the upper and deeper basin. The same convection 

 currents which we have described will take place here, 

 giving us a surface current from the ice, and an under 

 current towards the ice, now the water in finding its way 

 under the ice to the outlet, will take the easiest way possible, 

 and as it will find itself retarded or opposed at the surface 

 near the ice edge, and assisted near the bottom by the 

 convection circulation, its supply will be delivered by 

 preference as an under and therefore comparatively warm 

 current. Off the edge of the ice I found the water at 8^ 

 fathoms 37*2°, and in \']\ fathoms 37-4° F. In accordance 

 with the same principle of greatest easiness, this water 

 would penetrate into the frozen basin by the deepest exist- 

 ing channel. The lower or frozen basin is separated from 

 the upper and open one by a remarkable chain of islands 

 separated from each other by channels everywhere less 

 than there, and indeed hardly anywere more than two 

 fathoms deep. The two channels however next the main 

 land are each five fathoms deep, and it is through them 

 that the bulk of the water finds its way. This was shown 

 in a very singular way by the existence of a space of open 

 \vater stretching from the main land to the nearest island 

 over the shallowest part of the channel on the Dumbarton- 

 shire shore, there being thick strong ice over the deep 

 water on both sides. In its passage over the ridge which 

 rises very steeply, the warm water is thrown up near the 

 surface and its supply is sufficient not only to preserve 

 this space of open water, but also to raise the temperature 

 of aU the water of a depth greater than five fathoms in the 

 lower basin. 



In the case then of a lake only partially frozen, the 

 temperature of the water under the ice is lowered by the 

 drainage entering where it is frozen and is raised by the 

 water supplied from the open part provided the channels 

 connecting the two parts are not too shallow. 



In Linlithgow Loch which was entirely frozen over, the 

 very great rise of temperature near the bottom was caused 

 by the immense quantity of filth contained in its water and 

 in the mud at the bottom. J. Y. Buchanan 



ON THE BURSTING OF THE GUN ON BOARD 

 THE THUNDERERS 



IN the interval which elapsed between the bursting of 

 the gun and the report of the Committee much 

 thought and some trouble has been expended in divining 

 the possible causes which might, under one set of circum- 

 stances or another, have led to such a result. It now 

 appears, however, that, different as have been the various 

 suggestions, they all resembled each other in one particu- 

 lar, namely, that they were all wrong. 



It is to be hoped, however, that all the ingenuity that 

 has been expended will not have been thrown away, and 

 that some improvement may result from the pointing out 



' Read before the Lit. and Phil. Society of Manchester on February i8, 

 by Prof. Osborne Reynolds, F.R.S., Prcfessor of Engineering, Owens 

 College, Manchester. 



of such numerous defects. That in some respects, such 

 as the increasing twist and the sudden steps or shoulders 

 on the outside of the gun, the present system is defective, 

 is shown quite apart from the recent accident ; and al- 

 though it now appears that the moving forward of the 

 shot as the rammer was withdrawn had probably nothing 

 to do with this accident, it cannot be considered satisfac- 

 tory that this moving forward should be so much the rule 

 as it is shown to have been in the experiments recently 

 undertaken. 



Although at first sight it may appear that the fact of 

 the gun having been loaded with two charges of powder 

 and two shot is amply sufficient to explain the bursting, 

 it may not be useless to examine somewhat closely into 

 what would result under such circumstances. The bursting 

 of a 38-ton wrought-iron gun is an experiment of whick 

 we should make the most as we cannot expect to have it 

 often repeated. 



From the first accounts of the accident it appeared as 

 though the gun had simply broken in two, like a carrot, 

 at the first step, and that the front half had gone into the 

 sea. Such a failure Avould not have implied an excess of 

 pressure. It might have been caused by a great end 

 strain such as would have resulted had the shot jammed 

 when in full career and carried away the fore part of the 

 gun, or it might have resulted from the gradual weakening 

 of the section of the gun at the shoulder owing to the 

 different degrees of expansion immediately before and 

 immediately behind. One or other of these causes ap- 

 peared to afford the most probable explanation of the 

 phenomena as described in the early accounts. In various 

 subsequent reports, however, it was stated that fragments 

 of the fore part of the gun were blown about in all direc- 

 tions. So that the gun, instead of having simply broken 

 in two, must have burst like a shell in front of the first 

 shoulder. This fact placed the phenomena in an alto- 

 gether different light. The explosive bursting of the zone 

 of the gun into fragments implied an enormous excess of 

 pressure at this point of the gun. 



In order to cause the tube of the gun to burst longi- 

 tudinally at all would require several times the normal 

 pressure, and the breaking up of the wrought-iron tube 

 into fragments would show that the force was largely 

 in excess of what was necessary to burst it. 



After seeing these reports it appeared certain that the 

 gun had been subjected, at the point of rupture, to a 

 pressure enormously excessive, and the question became 

 whence could such a pressure have arisen ? To rne it 

 appeared that nothing short of such an action as might, 

 with a detonating fuse, result from the explosion of gun- 

 cotton or dynamite would explain the breaking of the 

 gun into fragments. Had the shot become jammed the 

 pressure might have been raised sufficiently to burst the 

 gun, but with pebble powder even this seemed doubtful, 

 and such an action seemed altogether inadequate to 

 explain the breaking of the gun into fragments. It 

 appeared, therefore, that there was but one conclusion to 

 be drawn — there had been something abnormal in the 

 loading. Had the gun been loaded with small grained 

 powder, gun-cotton, or dynamite, instead of pebble 

 powder, such a result might have been produced ; but 

 then, the gun would, if it had burst, have burst at the 

 breach unless the shot had slipped forward, and that 

 there should have been two accidents appeared highly 

 improbable. Besides, it was necessary to consider what 

 sort of a mistake was most likely to have occurred ; and 

 the only possible mistake that could have been made on 

 the spot appeared to be that of double loading. 



The fact that if two complete charges were put into the 

 gun, the powder of the second charge would be directly 

 beneath the point of rupture appeared in favour of this 

 the easiest mistake. But would, supposing the powder 

 to have been pebble powder, the pressure from the two 

 charges have been sufficient to cause the result ? At first 



