April 12, 1875] 



NATURE 



495 



\ the obscure heat-rays from copper at 100°, passing through 

 glass, produce a deflection on the scale of 3'25, whilst 

 under the same circumstances no current is detected in 

 the thermo-pile. The following substances are used as a 

 ! screen, and the deflections produced, when the source of 

 \ radiation is magnesium-wire, a standard candle, copper 

 at 400° and copper at 100°, are tabulated : — 



Rock-salt, 20 minims, thick ; rock-crystal, 42 millims. 

 thick ; dark smoky talc ; plate gbss of various thick- 

 nesses, both white and green ; a glass cell containing 8 

 millims. of water ; a plate of alum 5 millims. thick ; calc- 

 spar, 27 millims. thick ; ammonio-sulphate of copper, 

 opaque to rays below E, ditto opaque to rays below G. 



Mr. Crookes considers that these experiments show 

 that the repulsion is not entirely due to the rays usually 

 called heat, i.e. to the extreme- and ultra-red of the spec- 

 trum. Experiments have been tried with the electric and 

 the solar spectrum formed with a quartz train, which 

 prove the action to be exerted by the luminous and ultra- 

 violet rays. Some numerical data have been obtained, 

 but unfavourable weather has prevented many observa- 

 tions being made with the solar spectrum. 



The barometric position of the neutral point dividing 

 attraction from repulsion is next discussed. The position 

 of this point varies with the density of the substance on 

 which variation falls, the ratio of its mass to its surface, 

 its radiating and conducting power for heat, the physical 

 condition of its surface, the kind of gas filling the appa- 

 ratus, the intensity of radiation, and the temperature of 

 the surrounding atmosphe.e. The author is inclined to 

 believe that the true action of radiation is repulsion at 

 any pressure, and that the attraction observed when the 

 rarefaction is below the neutral point is caused by some 

 modifying circumstances connected with the surrounding 

 gas, but not being of the nature of air-currents. The 

 neutral point for a thin surface of pith being low, whilst 

 that for a moderately thick piece of platinum being high, 

 it follows that at a rarefaction intermediate between these 

 two points pith would be repelled, while platinum was 

 attracted by the same beam of radiation. This is proved 

 experimentally ; and an apparatus showing simultaneously 

 attraction and repulsion by the same ray of light is de- 

 scribed and illustrated in the paper. 



Mr. Crookes concludes his paper with a discussion of 

 the various theories which have been adduced in explana- 

 tion of these phenomena. The air-current and electrical 

 theory are considered to have been abundantly disproved. 

 The following experiment is given to show that Prof 

 Osborne Reynolds's hypothesis of the movements due to 

 evaporation and condensation at the surface will not 

 account for all the facts of the case, and that, therefore, 

 he has not hit upon the true explanation. A thick and 

 strong bulb was blown at the end of a piece of very diffi- 

 cultly fusible green glass, specially^ made for steam-boiler 

 gauges. In it was supported a thin bar of aluminium at 

 the end of a long platinum wire. The upper end of the 

 wire was passed through the top of the tube and well 

 sealed in, for electrical purposes. The apparatus was 

 sealed by fusion to the Sprengel pump, and exhaustion 

 was kept going on for two days, until an induction-spark 

 refused to pass across the vacuum. During this time the 

 bulb and its contents were several times raised to a dull 

 red heat. At the end of two days' exhaustion the tube 

 was found to behave in the same manner as, but in a 

 stronger degree than, it would in a less perfectly exhausted 

 apparatus, viz., it was repelled by heat of low intensity 

 and attracted by cold. A similar experiment was next 

 tried, only water was placed in the bulb before exhaus- 

 tion. The water was then boiled away in vacuo, and the 

 exhaustion continued, with frequent heating of the appa- 

 ratus to dull redness, for about forty-eight hours. At the 

 end of this time the bar of aluminium was found to behave 

 exactly the same as the one in the former experiment, 

 being repelled by radiation. 



It is impossible to conceive that in these experiments 



sufficient condensable gas or vapour was present to pro- 

 duce the effects Prof. Osborne Reynolds ascribes to it. 

 After the repeated heating to redness of the highest 

 attainable exhaus'ion, it is impossible that sufficient 

 vapour or gas should condense on the movable index 

 to be instantly driven off by the warmth of the finger 

 with recoil enough to drive backwards a heavy piece 

 of metal. 



Whilst objecting to the theories already advanced as 

 not accounting for all the facts of the case, Mr. Crookes 

 confesses that he is not as yet prepared with one to put in 

 their place. He wishes to avoid giving any theory on the 

 subject until a suflicient number of facts have been accu- 

 mulated. The facts will then tell their own tale. The 

 conditions under which they invariably occur will give 

 the laws, and the theory will follow without much diffi- 

 culty. 



THE FATAL BALLOON ASCENT 



'T*HE readers of Nature are no doubt aware of the 



^ fatal result of the recent ascent of the balloon Zenith; 



the following authentic details at first hand will no doubt 



be of interest : — • 



CiRON (Indre), April 17. 



The Zenith was sent up on the 15th of April in order 

 to determine the quantity of carbonic acid contained in 

 the atmosphere at an altitude of 24,000 feet. The " let 

 go " was given at twenty-five minutes to twelve a.m. 

 The captain was M. Sivel, and there were only two pas- 

 sengers, M. Gaston Tissandier and M. Croce-Spinelli. 

 The ascent took place gradually in a slight E. N.E. wind, 

 the sky being blue but vaporous. The rate of ascent was 

 calculated to be nine feet per second, but diminished 

 gradually. Shortly after one o'clock the altitude obtained 

 was 22,800, and the passengers were quite well, although 

 feeling weak. The inhalation of oxygen produced good 

 restorative effects when tried. Then a consjltation took 

 place, and the Zenith being in equilibrium, a quantity of 

 ballast was thrown overboard. M. Tissandier then fainted, 

 and is ignorant of what was felt by his friends. 



At eighteen minutes past two he was awakened by M. 

 Crocc-Spinelli warning him to throw over ballast as the 

 balloon was fast descending. He obeyed mechanically, 

 ;ind at the same time Crocd-Spinelli threw overboard the 

 aspirator, weighing eighty pounds. Tissandier then wrote 

 in his book a few disconnected words, and again fell 

 asleep for about an hour. When he awoke, the balloon 

 was descending at a terrific rate ; no more ballast was 

 left to be thrown away, and his two friends were suffocated. 

 Their faces had turned black, and the blood was flowing 

 from their mouth and nose. They were evidently dead. 

 It was a terrible situation. 



The only resource was to cut the grapnel rope a little 

 before the instant when the car should strike the ground, 

 which Tissandier did with astonishing coolness. The 

 wind had increased in strength, and Tissandier was 

 obliged to tear open the balloon in order to stop it. It 

 was caught on a hedee in a commune of Indre, called 

 Ciron, 190 miles S.S.W. from Paris. 



The tragic fate of Sivel and Spinelli is to be ascribed 

 to the fatal resolution of accomplishing, at any price, a 

 height of 24,000 feet, but mainly, no doubt, to the throw- 

 ing out of the aspirator, which will be discovered some- 

 where perhaps unbroken, as it had been provided with 

 a parachute.* 



The only instruments broken are the potash tubes for 

 the absorption of carbonic acid. The experiment had 

 been tried successfully ; two aspirators had been used, but 

 the tubes were not lodged in their proper case. 



Careful readings were taken with the thermometer, and, 



* According to the Times correspondent, tin's .ind other things have lieen 

 found. 



