492 



NATURE 



[Sept 5, 1878 



fegarded by military men as an important means of 

 reconnoitring. The Paris photographer and aeronaut, 

 Nadar, was successful on several occasions in securing 

 photographic records from balloons, but he never -pvib- 

 \ishidh\s modus operandi J and the problem of balloon 

 photography is one which still excites a good deal of 

 attention, Mr. Walter Woodbury, the well-known in- 

 ventor of Woodburytype — the only practical photo- 

 engraving process we know — submitted, during the last 

 war, to the Russian government, a very ingenious method 

 of securing pictures at an altitude. By his plan no one 

 ascends with the balloon at all, and therefore the latter 

 may be of very limited dimensions. It is captive, and 

 twisted into the tethering rope are insulated wires in con- 

 nection with a camera. The camera is weighted and 

 hung upon a pivot so as to be always horizontal, and a 

 fa^ attached to the balloon prevents the same from 

 gyrating. It is easy to understand how a lens may be 

 capped and uncapped from below with the aid of an 

 electric current, and the photographs are secured — for a 

 series may be taken at one ascent — upon a length of 

 sepsitive tissue which is unrolled for use through the 

 medium of clockwork. The sensitive tissue and roller 

 arrangement is that of M. Warnerke, which is known to 

 all dry plate workers, and which permits of securing 

 pictures without glass. Mr. Woodbury's invention has, 

 so far, been tested only in respect to its photographic 

 properties, but in cases where an aeronaut would run too 

 much risk, or where a large supply of gas is not available, 

 the apparatus would be well worthy of trial. 



It is the difficulty of securing a sufficiency of gas for 

 inflation that at present stands in the way of employing 

 balloons in the field. The PYench balloons are all large 

 ones, for they were constructed most of them for postal 

 service during the siege, and, besides the mails and 

 aeronaut, sometimes carried three passengers. With the 

 exception of half-a-dozen, all the balloons which left 

 Paris had a uniform capacity of 2,000 cubic metres, 

 while one, in which M. de Fonvielle and three other 

 persons travelled from Paris to Louvain, measured 3,000 

 metres. Such bulky balloons as these are unsuited for 

 the field, where the problem is to send a single observer 

 aloft with the minimum amount of time and trouble. The 

 smallest balloon and the lightest gas for the purpose are 

 what the soldier seems to require, and it is towards these 

 two points that attention has lately been directed by 

 Capt. Templar and the other officers who are just now 

 occupied in the study of aerial navigation in this country. 

 Naturally enough, hydrogen holds out the most promising 

 features as a lifting medium, and it is with this gas that 

 experiments are once more to be made. As our readers 

 remember, the weight of hydrogen is calculated to be 

 2*14 grains per 100 cubic inches, while air on the other 

 hand weighs 31 grains ; and, as the lifting power is re- 

 presented by the difference between these numbers, it 

 stands to reason that theoretically, a balloon, if filled with 

 hydrogen, need be of but comparatively very small dimen- 

 sions. Unfortunately, in a practical affair like balloon- 

 ing, a lot of accidental matters require to be taken into 

 , consideration, and two of these are the facts that it is diffi- 

 cult tosecure pure hydrogen, and more difficult still to keep 

 it in the balloon envelope when secured. Capt. Templar 

 is sanguine that a 10,000 cubic feet balloon is quite 

 capable of lifting an observer high enough for recon- 

 noitring purposes, if filled with hydrogen, and well-nigh 

 proved his case the other day when he overcame gravity, 

 if he did not rise, with the aid of a light coal-gas with 

 which this small balloon was filled. The coal-gas, 

 specially manufactured for his balloon, had a lifting- 

 power of 50 lb. per 1,000 feet, so that a total of 500 lb. 

 was here at his disposal. As we have said, this was in- 

 sufficient for an ascent, for, besides the weight of the 

 aeronaut, there are, it must be remembered, envelope, 

 car, tackle, cable, and ballast to be taken into considera- 



tion. Instead of 500 lb., hydrogen of the same volume 

 would have supplied a lifting-power of 700 lb., and this 

 of course would have been ample, and to spare, for an 

 ascent. 



To make this hydrogen recourse will be had, as in 

 previous experiments undertaken by our military autho- 

 rities, to the decomposition of water in the form of steam. 

 The latter is to be passed through tubes filled with iron 

 filings or turnings, and these, in becoming oxidised, set 

 free the hydrogen. Unfortunately the hydrogen obtained 

 in this way is impregnated with moisture, and unless sub- 

 mitted to the action of some desiccating agent like quick- 

 lime, for instance, is of little good for ballooning. The 

 hydrogen it is proposed to obtain in the field, at any rate, 

 in this fashion, and it remains to be proved whether Capt. 

 Templar and his colleagues can secure it sufficiently pure 

 and in proper quantity under these practical conditions. 

 Although hydrogen is given off fast enough at the outset, 

 previous experimenters have found the supply to fall off 

 rapidly, for as soon as the surface of the particles becomes 

 oxidised the decomposition of the steam ceases. 



But perhaps the most interesting feature of the present 

 ballooning experiment will be the trial of compressed gas. 

 As our readers know very well, compressed gases are now 

 a commercial article in this country, and you may pur- 

 chase cylinders of oxygen or hydrogen at twenty atmo- 

 spheres pressure. As our Royal Engineers carry about 

 Avith them in the field such unwieldy things as pontoons, 

 they can hardly grumble at a waggon load of hydrogen 

 tubes, and with these it is suggested to fill a balloon just 

 wherever a reconnaissance is to be made. On nearing 

 the enemy the first convenient spot will be chosen for the 

 manufacture of the hydrogen, and this will then be com- 

 pressed, with the assistance of suitable apparatus, into the 

 tubes, to be drawn off again when the ascent is to be 

 made. In this way there is always to be gas at hand not 

 only to fill the balloon but to keep up a constant supply 

 for a limited period, since hydrogen, under the most 

 favourable circumstances, rapidly exudes from a balloon 

 envelope. 



A military balloon, it appears to be decided, must be a 

 captive one, and opportunity would of course be taken 

 to place the observer in electrical communication with 

 the earth through the medium of insulated wires twisted 

 round the rope in the same way as in Mr. Woodbury's 

 photo-aerial apparatus above described. 



H. Baden Pritchard 



HYPNOTISM 



THE phenomena of "hypnotism," "mesmerism," o? 

 "electro-biology," have of late years excited so 

 much popular- interest — not to say popular superstition — 

 that their investigation by a competent man of science 

 will appeal to the sympathies of a wider public than the 

 purely scientific. My object, therefore, in writing the 

 present article is to give a brief review of a monograph 

 on this subject, which has just been published by the 

 well-known physiologist, W. Preyer of Jena.' 



In order to eliminate all possible effects of the imagina- 

 tion, Preyer performed his experiments only upon animals, 

 and he begins his paper with an historical sketch of 

 previous investigations of a similarly restricted nature. 

 First we have the "Experimentummirabile" of the Jesuit 

 Athanasius Kircher, published by him in the year 1646.2 

 This consists in taking a common fowl, binding its feet 

 together, and placing it on a floor. As soon as it has 

 ceased to struggle a straight line of chalk is drawn from 

 the point of its bill along the floor. If the legs are now 



' Die Kataplexle und der thierlsche Hj^notismus. (Gustave Fischer, Jena, 

 1878.) 



"^ In a postscript Preyer states that he has found this experiment to have 

 been pubHshed ten years earlier, by Daniel Schwenter, and the quotation 

 which he makes from Schwenter's book goes to prove that Kircher probably 

 derived his knowledge of the experiment from that source. 



