396 



NATURE 



[August 23, 1900 



pattern instrument and no comparable apparatus have been intro- 

 duced. He admits that the Seismological Committee of the 

 British Association have taken a step in the right direction, but 

 considers that the instrument used by them possesses several 

 defects which prevent its general adoption. The conditions 

 which should be satisfied by the type apparatus, he describes as 

 follows : It must be astatic or possess a stationary mass, and 

 must be equally capable of recording the very small and rapid 

 preliminary vibrations and the subsequent undulations of long 

 period ; it must have the sanction of experience, the cost of 

 erection and maintenance must be small, and the construction 

 so simple that it does not easily get out of order ; it must allow 

 the continuous inspection of the traces, and its sensibility must 

 lie within convenient limits. 



About two years ago Dr. Sambon brought forward evidence 

 that sunstroke was an infectious disease, and consequently due 

 to microbic influences. This view has not met with general 

 acceptance, and Mr. E. H. Freeland, who has had exceptional 

 opportunity of observing cases of sunstroke, both ashore and 

 afloat, shows in the Middlesex Hospital Journal (July) that 

 all the phenomena of this aff'ection can be explained on general 

 physiological principles without reference to germs at all. He 

 concludes his paper as follows : — "Whether sunstroke be due 

 to external physical causes, or whether it be an infectious 

 disease and due primarily to a micro-organism which has yet to 

 be isolated, must be decided in the future. For the present it 

 seems to me that there is ample evidence for believing that 

 sunstroke is due primarily to thermic influences — the exposure 

 of the body to a hot moisture-laden atmosphere — and secondarily 

 to the circulation in the blood of certain toxic poisons, the re- 

 sult of perverted tissue metabolism ; and that, until more tangible 

 evidence is brought forward to prove that the aff"ection is due to 

 microbic influence, one may safely accept the older doctrine 

 with regard to its causation as a sound working hypothesis, if 

 nothing else." 



Prof. F, E. Nipher, of Washington University, St. Louis, 

 Missouri, has sent some further particulars with reference to the 

 methods he uses to obtain a " zero " plate. His observations 

 upon photographic reversal have already been noticed in these 

 columns (pp. 62, 159), and he has pointed out the bearing of 

 his work upon eclipse photography (p. 246). The following 

 details of the operations he follows may enable other photo- 

 graphers to repeat his experiments. " The plate is placed 

 under a punched stencil in a printing frame. It is exposed at 

 /cm. from a 16 c.p. lamp. By a few trials one can find the 

 time-interval of exposure, so conditioned that nothing will 

 develop on the plate in a developer of fixed composition, 

 strength and temperature, and at a fixed distance from the 

 16 c.p. lamp. This is a standard developer. With a shorter 

 time of exposure than that giving the zero plate, a negative 

 will result, and with a longer time, a positive. A plate to be 

 used in taking any picture to be developed in the standard 

 developer (as a positive) is all exposed to the 16 c.p. light at a 

 distance / cm. for a time which experiment has shown will put 

 the film into the zero condition when developed in the standard 

 bath. It is then put into the plate-holder, and given a camera 

 exposure in the usual way, after which it is developed. It is not 

 important that the developing bath should be at any particular 

 distance from the lamp. The plate is to be pre-exposed so that a 

 zero plate will result in that particular bath, at any fixed 

 distance from the lamp. I usually make this distance about 

 eight inches." 



According to Maxwell's electromagnetic theories, a moving 

 body charged electrically produces a magnetic field. In the 

 BiiUetin of the French Physical Society, M. V. Cremie.u 

 NO. 1608. VOL. 62] 



gives a brief note on certain experiments destined to test the 

 actual existence of such a field, as well as the converse result 

 that a moving charge placed in a variable magnetic field 

 experiences a certain ponderomotive force. Having, at the 

 suggestion of M. Lippmann, conducted some experiments for 

 the purpose of investigating the latter effect, with ' negative 

 results, M. Cremieu now gives an account of certain investi- 

 gations made with a disc of 37 cm. in diameter, rotating at the 

 rate of 100 to 130 revolutions per second in the centre of an 

 annular coil connected with a highly sensitive galvanometer. 

 If the disc is suddenly charged, the convection current thus 

 produced should give rise to an induced current through the 

 galvanometer, and the magnitude of the convection current being 

 determined by the number of revolutions and the density of the 

 charge, the amount of the expected deflection of the galvano- 

 meter could be calculated. No deviation of the predicted magni- 

 tude was obtained, and the author concluded that a moving 

 charge does not produce a magnetic field. Such a conclusion 

 leads logically to the rejection of existing theories of the electric 

 current, and M. Cremieu proposes to conduct further experi- 

 ments with the object of throwing more light on this difficult 

 question. The author does not, in this note, say anything 

 about the effects of the self-induction of the rotating disc, and 

 further information on this point appears desirable in criticising 

 the results. 



A FEW interesting details referring to the use of wireless 

 telegraphy in the French navy are given by a naval correspon- 

 dent of the Daily Graphic. It is stated that half-a-dozen ships 

 in the combined French squadron recently at Cherbourg were 

 fitted for wireless telegraphy, and the clicking, crackling, and 

 sparking of the big coils was heard on board all day. Messages 

 have been taken in and sent out at distances quite twice or three 

 times as great as anything achieved with the instruments in use 

 in the British ships. The French do not fit the wire to a gaff" as 

 in our ships ; it is suspended between the funnels to the triatic 

 stay, and is much less conspicuous. The manoeuvring of the 

 submarine boats, Morse and Narval, is described as marvellous ; 

 they are, it is stated, much ahead of the American Holland bosii, 

 which is considered to be a formidable weapon. 



An interesting and detailed account of Count von Zeppelin's 

 successful trial trip of his navigable balloon on July 2 is given in 

 Die Uinschaii by an anonymous author, who has endeavoured to 

 dispel the somewhat exaggerated reports which have been 

 circulated as to the success or failure of the experiment. It is 

 pointed out that the delay in the ascent, which some persons 

 attributed to an accident, was really caused by the wind being 

 too strong at the tima originally proposed for the trip. The 

 wind-velocity at the time of starting was 5 5 metres per second, 

 and the balloon was actually driven forwards for a short distance 

 in the face of this wind. But after a short time the path deviated 

 till it made an angle of 30° with the wind-direction. This 

 deviation, the writer explains, was due to several causes. In 

 the first place the rope broke which supported the movable 

 mass necessary for the maintenance of longitudinal balance, and 

 to restore equilibrium it was necessary to stop or even reverse 

 one of the machines, so that the balloon could no longer be 

 driven full ahead. Moreover, the framework was found to have 

 undergone a little deformation, which gave the machine a slight 

 bias to one side, interfering with the steering. The wind causing 

 the balloon to drift towards the shore, a descent was made in 

 order that Count Zeppelin might land on the water (to use an 

 Irishism), and thus have his machine towed back by steamer. 

 The descent was very gradual, the cars gently sinking down to 

 the water without the sudden jerk which is commonly experienced 

 in an ordinary balloon. This result is attributed to the favour- 



