?66 



NATURE 



\August 19, 1S80 



by a trustworthy observer, seems to imply a discharge 

 over a totallcngth of nearly ten miles. 



When a tree is struck by a violent discharge it is usually 

 split up laterally into mere fibres. A more moderate 

 discharge may rupture the channels through which the 

 sap flows, and thus the tree may be killed without sufter- 

 ing any apparent external damage. These results are 

 usually assigned to the sudden vaporisation of moisture, 

 and the idea is probably accurate, for it is easy to burst a 

 very strong glass tube if we fill it with water and dis- 

 charge ajar by means of two wires whose extremities are 

 placed in the water at a short distance from one another. 

 The tube bursts even if one end be left open, thus show- 

 ing that the extreme suddenness of the explosion makes 

 it act in all directions, and not solely in that of least 

 resistance. When we think of the danger of leaving even 

 a few drops of water in a mould into which melted iron is 

 to be poured, we shall find no difficulty in thus account- 

 ing for the violent disruptive effects produced by lightning. 



Heated air is found to conduct better than cold air, 

 probably on account of the diminution of density only. 

 Hence we can easily see how it is that animals are often 

 killed in great numbers by a single discharge, as they 

 crowd together in a storm, and a column of warm air 

 rises from the group. 



Inside a thundercloud the danger seems to be much 

 less than outside. There are several instances on record 

 of travellers having passed tlu'oiigli clouds from which, 

 both before and after their passage, fierce flashes were 

 seen to escape. Many remarkable instances are to be 

 found in Alpine travel, and specially in the reports of the 

 officers engaged in the survey of the Pyrenees. Several 

 times it is recorded that such violent thunderstorms were 

 seen to form round the mountain on which they were en- 

 camped, that the neighbouring inhabitants were surprised 

 to see them return alive. 



Before the use of lightning-rods on ships became 

 general great damage was often done to them by 

 lightning. The number of British ships of war thus 

 wholly destroyed or much injured during the long v/ars 

 towards the end of the last and the beginning of the 

 present century is quite comparable with that of those 

 lost or injured by gales, or even in battle. In some of 

 these cases, however, the damage was only indirectly due 

 to lightning, as the powder magazines were blown up. In 

 the powder magazine of Brescia, in 1769, lightning set fire 

 to over 2,000,000 lbs. of gunpowder, producing one of the 

 most disastrous explosions on record. 



A powerful discharge of lightning can fuse not only bell 

 wires, but even stout rods of iron. It often permanently 

 magnetises steel, and in this way has been the cause of 

 the loss of many a good ship ; for the magnetism of the 

 compass-needles has been sometimes destroyed, sometimes 

 reversed, sometimes so altered that the compass pointed 

 east and west. And by the magnetisation of their steel 

 parts the chronometers have had their rates seriously 

 altered. Thus two of the sailor's most important aids to 

 navigation have been simultaneously rendered useless or, 

 what is worse, misleading ; and this, too, at a time when, 

 because of clouds, astronomical observations were generally 

 impossible. All these dangers are now, however, easily 

 and all but completely avoidable. 



A very singular effect of lightning sometimes observed 

 is the piercing of a hole in a conducting-plate of metal, 

 such as the lead-covering of a roof. In such a case it is 

 invariably found that a good conductor well connected 

 with the ground approaches near to the metal sheet at the 

 part perforated. 



{To be conliiuied.) 



HUMAN HYBERNATION 

 T^R. TANNER is scarcely oft' the field when another 

 J-^ _ physiological wonder breaks out in the form of a 

 sleeping girl of Grambke, near to Bremen. This young 



lady lies, it is said, in a profound slumber night and day, 

 resting on her left side and never asking for food, but 

 swallowing liquid food when it is put into her mouth. The 

 trance lasts an average of fifty days, during which time 

 she is pale, but does not lose in weight. Her sleep is not 

 cataleptic in the proper sense of the term, inasmuch as she 

 is sufficiently conscious to swallow, and presents none of 

 the indications of death. She merely sleeps. Instances 

 of this kind are not so uncommon as those of true cata- 

 lepsy, though some of them are sufficiently remarkable. 

 In the Transactions of the Royal Society Dr. W. Oliver 

 has recorded the history of an extraordinary sleeping 

 person named Samuel Chilton of Tinsbury, near Bath, 

 who, on May 13, 1694, being then "of robust habit of 

 body, not fat, but fleshy, and a dark brown hair," hap- 

 pened, without any visible cause or evident sign, to- 

 fall into a veiy profound sleep, out of which no art 

 used by those who were near him could rouse him 

 until after a month's time ; then he rose of him- 

 self, put on his clothes, and went about his business 

 of husbandry as usual; slept, could eat and drink as 

 before, but spoke not one word till about a month 

 after. In 1696, on the 9th of April, this youth fell 

 off to sleep again, and although a heroic apothecary, 

 INIr. Gibbs, bled him, blistered him, cupped him, and 

 scarified him, he slept on for seventeen weeks, waking 

 up on August 7, not knowing he had slept above a 

 night, and unable to be persuaded he had Iain so long, 

 until going out into the fields he found everybody busy 

 getting in the harvest, and then remembered very well 

 that when he fell asleep they were sowing of the barley 

 and oats which he now saw ripe and ready to be cut 

 down. For six weeks of this sleep he had fasted, but 

 after he awoke he went to work in his ordinary way, and 

 continued to work until August 17, 1697, when, after 

 complaining of shivering and cold in his back, and 

 vomiting once or twice, he fell into one of his long sleeps 

 once more, and being visited by Dr. Oliver and many 

 others, was subjected to further bleeding and extremely 

 sharp treatment indeed, but without being roused. S» 

 he lay sleeping until November 19, when he awoke, said 

 he " felt very well, thank God," ate some bread and 

 cheese, and dropping off" still another time, slept on until 

 the end of January, 1698, and "then waked perfectly 

 well, not remembering anything that happened all this 

 while." He was observed to have lost flesh, but only 

 complained of being pinched by the cold, and presently 

 fell to husbandry as at other times. The known pheno- 

 menon that is nearest to this is hybernation in some of 

 the inferior animals ; but it is worthy of remark that 

 the persons affected take food unconsciously w'hen it is 

 offered them, the lower nervous cenfi'es seeming to 

 remain in a continued state of activity. 



PHYSICS WITHOUT APPARATUS'" 

 III. 



THE laws of the behaviour of liquids, their pressure 

 and their flow, are very readily demonstrated without 

 special apparatus by the aid of simple articles of every- 

 day use. First amongst the laws of liquid pressure comes 

 the all-important principle that the pressure exerted by a 

 liquid at any point is proportional to the depth, below 

 the surface, of the point under consideration. This 

 pressure is exerted upwards or downwards according to 

 circumstances. We can show first a case of pressure 

 exerted in an upward direction. Take the glass chimney 

 of a lamp, that of a paraffin-lamp will answer, though 

 the straighter form of chimney used in an Argand or a 

 Silber lamp is preferable. Cut out with a pair of scissors 

 a circular disk of stout cardboard, and attach a thread to 

 it by means of a drop of sealing-wax. Provide yourself 

 also with a deep dish of water. Such a glass trough as is 



' Continued from p. 345. 



