114 



KNOWLEDGE 



[May 2, 1898. 



A BRILLIANT METEOR. 

 To the Editors of Knowledge. 



Sirs, — Last night at 10.20 I saw an extremely brilliant 

 meteor, ■which appeared a little south and east of Procyon, 

 and disappeared quite at the zenith. In spite of the bright 

 moonlight it was a very conspicuous object of bluish white 

 colour ; its course appeared (perhaps from my point of 

 view) to be quite straight, and occupied about five or six 

 seconds of time. It seemed simply to " go out " at last, 

 without explosion, sparks, or anything else. 



April Cth, 1898. G. Northover Stretton. 



MERCURY. 

 To the Editors of Knowledge. 



Sirs, — I think it may possibly interest some of your 

 readers to know that I observed Mercury to-night, un- 

 assisted, except by a mental knowledge of its R.A. and 

 Dec, at the short interval of seven minutes only after 

 sunset, from my window at King's Cross. Is not this a 

 record for a London view ? It was conveniently observ- 

 able until 7.50 P.M., except at infrequent intervals, when 

 it was obscured by stray clouds. C. B. Holmes. 



April 12th, 1898. 



P.S. — It was between three and four minutes to seven 

 when it first revealed itself. 



NATURE'S FINER FORCES. 



SOME NOTES ON OLD WORK AND NEW 



DEVELOPMENTS. 



By H. Snowden Ward, f.r.p.s., Editor of " The 



Photogram." 



IT is rather difficult to find a title for an entirely new 

 subject which is still in its early days of investi- 

 gation, and to which its pioneer has given no name, 

 it is all the more difficult when three or four un- 

 authorized persons have undertaken to christen the 

 subject, when its scientific basis is uncertain, and when 

 there is a suspicion that it may be closely allied to an 

 older class of results which have a recognized title. The 

 subject of the Bakerian Lecture before the Royal Society 

 this year is extremely interesting, because it opens up a 

 field of investigation in which the results are surprising 

 and curious, while the methods are so simple and the 

 requisites are so cheap that it is possible for anyone to 

 take up the work and to carry the results a few stages 

 further. 



Dr. W. J. Russell gave his lecture the non-committal 

 title of " Experiments on the Action exerted by Certain 

 Metals and Other Bodies on a Photographic Plate " ; and 

 journalists who have recorded his results have given the 

 subject such titles as Scotography (apparently because 

 this is the name of a method of teaching the blind to 

 write), Vapography (because the phenomena may be the 

 result of vapour given off from the metals, etc.), and other 

 equally appropriate titles. 



Before dealing with Dr. Russell's observations it may 

 be well to recall one or two older phenomena which do 

 not seem to have been referred to in the discussion on 

 Dr. Russell's lecture, but which may have a distinct con- 

 nection with his work. 



A common phenomenon, familiar to students, and even 

 to many schoolboys, is the formation of " breath figures " 

 upon a mirror, a piece of plate glass, or, better still, a 

 polished metallic reflector. On the polished surface, which 

 should be cold, lay any small object such as a coin. While 

 this is in position breathe on the polished surface. After- 



wards, for days and sometimes even for weeks or months, 

 the image of the object may be restored by again breathing 

 upon the polished surface ; and this may be done re- 

 peatedly, even though the surface be well cleaned and 

 polished. 



A possibly kindred efi'ect may be seen on windows to 

 the inside of which a printed placard has been affixed. 

 Though the printing ink does not touch the glass, it will 

 be found, after the placard has been exposed for some time, 

 that the window has acquired the property of condensing 

 moisture on the parts near the printing ink of the placard 

 differently from its condensation on other parts. And 

 this property will remain for weeks or months, through 

 repeated cleanings of the window. 



In the early forties, M. Moser, of Konigsberg, and 

 Robert Hunt, the British investigator on light, reported 

 some extremely interesting experiments on the eflects of 

 contact between various substances and polished metallic 

 plates ; and after long, patient research Hunt attributed the 

 results to difference of temperature, and called the process 

 Thermography. He even went so far as to anticipate that 

 the process might prove more valuable than photography 

 when fully developed. 



Hunt, working in the days of the Daguerreotype, when 

 the photographic image was developed upon a metalhc 

 plate by means of vapours, applied the same method to the 

 development of his thermographic images, with the result 

 that he got strong and permanent representations of the 

 objects laid upon his metallic plates. He found that 

 dissimilarity in the objects and the polished plates was 

 necessary ; for instance, gold and silver coins gave good 

 images on a copper plate, while copper coins did not act on 

 copper. He noted further that the mass of the receiving plate 

 affected the result, and that better images were made upon 

 a large than upon a small sheet of copper. Using various 

 pieces of glass, mica, tracing paper, etc., it was found that 

 while some of the glasses and the tracing paper gave 

 strong images, other glasses made little or no impression, 

 and the mica left no trace. It was found that some objects 

 of which no trace could be developed with mercury vapour 

 gave good images with the vapour of iodine. 



The later experiments bring us nearer to the results 

 shown on dry plates by Dr. Russell, for Hunt found that 

 objects separated from the metallic plate by air space of 

 half an inch, or more, were capable of strongly im- 

 pressing it after one night's exposure, and that a deal 

 box acted very strongly. Further, that printed paper 

 acted on the plate to such an extent that very good copies 

 of any printed matter could be made, and it was in this 

 direction that Hunt suggested the first practical applica- 

 tion of Thermography. 



Another set of observations, received with scorn by most 

 of the scientific men of their day, but confirmed in 1883 by 

 a committee of the Psychical Research Society, were those 

 of Reichenbach, on what he called " odic force," a property 

 which he found to emanate from almost aU substances. 

 Most of Reichenbaeh's observations were made by means 

 of sensitive patients, who stated that they could see 

 luminous emanations from various metals, etc. ; and it is 

 unfortunate that he did not carry out to a considerable 

 extent his experiments with photographic plates — on 

 which he did find results after the very few experiments 

 made. I mention Reichenbaeh's work because his patience 

 in research and verification was enormous, and his book 

 (" Researches on the Dynamics of Magnetism") is full of 

 reports of very suggestive experiments — researches which 

 might now be repeated with lenses and photographic dry 

 plates, with, perhaps, good results in the light of the recent 

 work of Dr. Russell. 



