October 22, 1896] 



NA TURE 



595 



I failed entirely to get any Xray results when only the usual 

 induction sparks bombarded tlie bulb, these sparks often 

 destroying the vacuum. My Tesla apparatus gives a spark three 

 inches long in air at normal pressure. The mica radiometer 

 vanes after many e.vpeiiments lost nearly all the black substance 

 with which they w ere coated ; it appeared in the form of a deposit 

 on the inside of the bulb, and it was deposited in the form of 

 concentric circles, the centres of which were situated exactly 

 opposite to the ends of the pointed conductors attached to the 

 Tesla coil. 



Thinking that the mica vanes in the Crookes' radiometer 

 might have played a considerable part in producing the X-ray 

 |ihotograph, I replaced the radiometer by a well-exhausted bulb 

 4 cm. diameter, made of .soda glass ; the bulb was placed with 

 respect to the conductors from the Tesla coil in the same position 

 as the radiometer in the former experiment. I found that with 

 the same exposure and distance, a good X-ray photograph of the 

 bones in the hand was produced. During the experiment the 

 bulb was lit up with a bright and yellowi.sh green glow. Since 

 the Tesla discharge rapidly produces ozonised air which is 

 irritating to the nose, throat and lungs, it is best to place the 

 terminals in a draught of air moving away from the operator. 



Oxford, October 17. Frederick J. Smith. 



Siemens's Domestic Gas Fire. 



H.\viX(; reference to the request, in your number of 

 September 17, for information on this subject, it is worthy of 

 remark that the chief feature in Sir William Siemens's inven- 

 tion, namely the general idea of using gas to aid the ordinary 

 tire (instead of applying it merely to heat inert material), is 

 capable of much simpler, cheaper, and more extensive appli- 

 cation than it has yet met with. Some such gas-aided fires, 

 which have answered well, will be found described in the 

 Builder of October 26, 1889. Their only difference from the 

 ordinary household fire consists in the introduction of a few 

 common gas jets among the fuel, which may be either coal or 

 coke, or, preferably, a combination of the two. 



The same idea may be applied in other ways. I lately saw, 

 in an artist's studio, a "gas torch," which was attached to a 

 flexible lube, and thrust between the bars when wanted. And 

 Prof. Ramsay, in a recent lecture, has proposed another 

 ingenious contrivance with the same object. In any case, the 

 ea.sy command which the gas gives over the general manage- 

 ment of the fire is a great domestic convenience. Its only 

 drawback is a temptation to indulge in a somewhat lavish gas 

 consumption. W. Pole. 



Athenaium Club. 



The 'Variable Star Z Herculis. 



In the issue of Nature for October i, a note appears on the 

 above variable, containing some important remarks on the 

 general practice of smoothing curves, and rejecting outstanding 

 ob.servations. I fully agree with Mr. Yendell, that by carrying 

 out this practice unduly, much valuable information may be lost. 

 During eleven years' continuous observations of long-period 

 variables, I have not rejected a single observation, and my light 

 curves are produced by simply plotting down the observations 

 (each of which is the mean of five comparisons with stars of 

 known magnitude) on a squared form, and joining the dots by 

 straight lines. The result has been to abundantly prove the 

 existence of very many secondary and minor variations, both in 

 the rise and fall of nearly all the stars under observation. 



Specially marked in.stances of complex variation of light 

 curve occur in the cases of R Aurig*, T Ursae Majoris, R 

 Draconis, and S Cephei. In many cases the magnitudes and dates 

 of maximum and minimum are very wide of the predictions; and I 

 am forced to the conclusion, arrived at in the case of Z Herculis, 

 " that the period of these stars must evidently be variable, 

 though the character and value of the variation cannot at present 

 be determined." CtJTHBERT Peek. 



Rous<lon Observatory, Lyme Regis, October 12. 



"Eozoon Canadensa." 

 Once more the long controverted point as to the organic origin 

 of this remarkable body was brought before Section C at the 

 meeting of the British Association at Liverpool, by that in- 

 defatigable naturalist, Principal Sir William Dawson, Montreal, 

 and which, as on all former occasions when brought before a 

 scientific audience, provoked considerable discussion both for and 



NO. 1408, VOL. 54] 



against. Amongst others, Prof. Bonney took part. There is 

 one remark that he made, which I beg of you to allow me to 

 emphatically contradict, /.(•. that the late Dr. Carpenter had 

 been deceived by the geologist who sent him sections of the speci- 

 mens from the West Highlands of Scotland. It was the writer 

 ot the present note who sent the sections referred to, and he 

 thought of contradicting the assertion of Prof. Bonney at the 

 time, but conceived it would be a gross abuse of politeness, not 

 only to Sir William Dawson, but also to the members of the 

 Section, to take notice of a matter so foreign to the subject under 

 discussion, and also from the conviction that Prof. Bonney must 

 have been misinformed. This is like the old story of the three black 

 crows which, from being black as a crow, got metamorphosed into 

 three black crows, feathers and all. The correspondence with 

 Prof. Carpenter and others is lying before me, but at present I 

 shall simply give a copy of my own letter that accompanied the 

 specimens, and which I hope will satisfy Prof. Bonney and 

 others that there is no truth in the assertion that I deceived Prof. 

 Carpenter, or any of the other naturalists who believed that the 

 structure was of organic origin. James Thomson. 



6 Stuart Street, Shawlands, Glasgow, October 2. 



{ Copy of letter referred to. ) 



April 22, 1876. 



Dear Sir, — Vou did me the honour, nearly two years ago, 

 to send me a type specimen of Eozoon Canadensa, in order that 

 I might know the characters of that fossil organism if I should 

 discover anything like it in the Highlands of Scotland. Since 

 then I have been through part of Argyllshire, Inverness-shire, 

 Ross-shire, Sutherlandshire, and Caithness-shire, and have at 

 last discovered in the neighbourhood of Tarbert Harris what 

 seems to me to be organic structure ; and the fact that the rocks 

 of that district have been described by Sir R. Murchison and 

 others as being of Laurentian age, suggests that the enclosed 

 specimens have some little interest, and more especially after the 

 article that appeared in the Annals of last month. [I then gave 

 a list of the names of the geologists and naturalists who had 

 examined the specimens, all of whom, with one exception, pro- 

 nounced the structure to be of organic origin. These names I 

 forbear to introduce at present, but will give the latter part of 

 the letter.] The parent rock is found interstratified with a dark 

 grey shale. About ten feet to the south of this .section there is 

 some very beautiful graphic granite in situ : a suite of the speci- 

 mens of which I procured. None of the graphic granite shows llie 

 beautiful structure that is seen in the intercellular spaces of the 

 enclosed. The outer margin of the mass from which the enclosed is 

 obtained approximates in external aspect to some of the varieties 

 of graphic granite, suggesting the problem : What is graphic 

 granite ? May it not be a highly metamorphosed organic body ?■ 

 the enclosed being less metamorphosed, hence the preservation 

 of the organic-like structure. Such seems to me probable, but 

 not having seen the graphic granites from other localities, I can- 

 not give an opinion, and will leave the solution of the problem 

 in your hands, and shall be pleased to hear your opinion at 

 your earliest convenience. 



I am, faithfully yours, 

 (Signed) James Thomson. 



To Prof. W. B. Carpenter, M.D., F.R.S., Sec, London. 



The Departure of the Swallows. 



LordHobhouse's observations with regard tothe "swallows,"" 

 would lead one to suppose that all the birds would have gone 

 away south before now ; Init yesterday I saw two swallows and 

 three martins hard at work flying about. This may not be very 

 late for the martin, but surely it is quite an unusual date for the 

 swallow, though White of Selborne records having seen them 

 as late as November 3, but does not say anything about the 

 martin. He adds to his record, " None [swallows] have been 

 observed at Selborne since October 11." E. P. 



Newnham. 



■Wasps and Flies. 



Many years ago I was in a country butcher's shop, and saw 

 several wasps occupied in cutting out and carryiiig oflT smaU 

 chunks of meat. (Kidney was most in demand, as being ' ' short " 

 in texture.) 



I pointed out the marauders to the butcher, and was told that 

 he was always glad to see wasps in his shop, as they kept the 

 bluebottles away. E. H. 



October 17. 



