April i6, 1S96] 



NATURE 



557 



does take place, independent evidence of it should be obtain- 

 able in the case of optically active substances by a change in 

 their rotatory power takinj; place when they are exposed to the 

 X-rays, as it is well known that the ionised molecules of active 

 compounds are possessed of very different activity from the un- 

 dissociated molecules themselves. To put this point to the 

 test, Mr. MacClregor and I have polarimetrically examined two 

 optically active compounds, ethylic dibenzoylglycerate and 

 methylic acetylglycerate, interposing a Crookes' focus tube 

 between the polarising Nicol and the column of active liquid ; 

 Imt although the discharge was maintained in both cases for 

 three-quarters of an hour, there was not the slightest change in 

 the rotation observable. To facilitate the passage of the rays, 

 we employed a thin microscope cover-glass to close the polari- 

 meter tube at the end nearest to the Crookes' tube, and that the 

 rays were actually traversing the column of active liquid was 

 demonstrated by obtaining a photographic effect at the other 

 extremity of the tube, whilst the efficiency of the Crookes* tube 

 was further proved by the favourite test of the skeletal photo- 

 graph of a hand, which yielded an impression of great sharpness 

 and exhibiting a most remarkable amount of detail. It would 

 appear, therefore, that the Rontgen rays either do not give rise 

 to any ionisation at all, or that the concentration of the ions is 

 >o small as not to be detectable by means of a sensitive polari- 

 meter. I have previously shown, in conjunction with Mr. Pickard 

 (Trans. Chein. Soc, 1896), that the active bodies in question 

 exhibit what appears to be a process of ionisation when dis- 

 solved in certain organic solvents, which process is accompanied 

 by a very conspicuous change in their rotatory power, so that 

 they appeared to be specially adapted for testing this suggested 

 influence of the X-rays. 



Incidentally we have roughly tested the relative opacity of a 

 number of organic compounds to these rays by spreading ap- 

 proximately equal thicknesses of each on a number of micro- 

 scope cover-glasses, which were placed on a photographic plate 

 enclosed in a black envelope, and then exposing them all 

 simultaneously to a Crookes' tube placed a few inches above. 

 (Jut of nearly forty organic compounds belonging to both the 

 fatty and the aromatic series, the only ones exhibiting any 

 marked opacity contained iodine, bromine, or chlorine, the 

 iodine compounds being the most and the chlorine compounds 

 the least opaque. Thus methyl iodide, ethyl bromide, ethylene 

 iodide, ethylene bromide, monobromacetic acid, tribromacetic 

 iicid. bromobenzoic acid, and trimethy'enebroinide were very 

 markedly o]iaque, and curiously monochloracetic acid was much 

 more distinctly opaque than either dichlor- or trichlor-acetic acid. 



iMason College, Birmingham. Pkkcv F. Frankland. 



Radiographs by Fluorescent Screens. 



It may perhaps interest those who occupy themselves in 

 [photographing with Rontgen rays to know that a very effective 

 and rapid method is obtained when proceeding as I will ex- 

 plain. I had a piece of scheelite or native tungstate of calcium, 

 >uch as occurs in a collection of minerals, crushed to a some- 

 what coarse powder, and made it into an emulsion with gela- 

 tine ; this was applied in a consistent and uniform layer on a 

 piece of stiff black paper, and after this was dried the surface 

 showed numerous crystalline, glittering particles. The right 

 condition for fluorescing was attained, as was evident, when a 

 Crookes' tube in action was placed behind and looked at in the 

 dark, though the luminosity was not so strong as with a screen 

 covered with crystals of platinocyanide of barium. The paper, 

 thus prepared, was simply laid down on a verj' sensitive photo- 

 graphic glass plate, with its fluorescent side of course in contact 

 with the film ; on the upper surface metallic objects or the 

 fingers were put. Applyuig now Newton's focus tube (which, 

 I may add, gave me excellent results in former experiments) 

 with an induction coil, regulated to give sparks of five to six 

 inches, I obtained sharply-defined radiographs of keys, <N;c., in 

 twenty-five seconds, and of the fingers, showing the bones and 

 metallic objects hidden between them and the plate, in ninety 

 seconds, distinct enough to perceive even the eye in a needle 

 that was put in the epidermis. I also tried the fluoride of 

 calcium mentioned by Prof Winkelmann, of Jena ; but I per- 

 ceived no fluorescence, perhaps because the powder was amor- 

 jihous throughout. As scheelite is a very cheap mineral, large 

 .screens with fluorescent surfaces may be constructed at a trifling 

 expense. L. Bl.EKKRODE. 



The Hague, April 6. 



NO. I 38 I, VOL. 53] 



Perhaps some of your readers who are practising electro- 

 graphy are not aware that those of them who possess a jxitassium 

 platino-cyanide screen can diminish their exposures to a quarter 

 of the time now necessary. I tried the experiment yesterday, 

 and have been more than pleased with the results. The modus 

 operandi is as follows. The screen is first laid on the dark- 

 room table, platino-cyanide uppermost. A celluloid rapid sen- 

 sitive film is then placed upon it, gelatine side downwards, and 

 in contact with platino-cyanide. Upon the top of all is placed 

 the hand or other object to be electrographed, and in contact 

 with the celluloid. The whole, including screen, celluloid film, 

 and object, are then raised from the table, and a light tight cloth 

 bag drawn over them and properly secured. This arrangement, 

 exposed under the Crookes' tube in the usual way, gives about 

 four times the speed attainable without the reinforcing action of 

 the screen. The " grain " of the screen shows ; but if the salt 

 has been finely powdered before preparing it, this is no great 

 objection. (Jlass-.'jensitive plates are of course inadmissible 



Oaklands, Chard, April 13. J. William Gifkord. 



Abnormal Rainbows. 

 O.N March 22, about 6 p.m., a rainsquall was pa.ssing south- 

 east of this station, and as the sun was shining clear and bright 

 in the opposite quarter of the sky, a rainbow soon appeared. 

 The colours were very brilliant, and a secondary bow was at 

 once seen. From the base of the primary bow a perfectly 

 straight vertical pillar arose of similar width, and the same 

 colours, arranged in similar order from right to left ; this was 

 quite as distinct, and persisted quite as long as the usual rain- 



Coa.st Guard .Station. 



bow, and the singular spectacle of the two rainbows with the 

 vertical shaft attracted considerable attention, and was noticed 

 by a large number of persons. It was described by several as 

 the V-shaped rainbow. The sketch, made by my assistant, Mr. 

 C. G rover, shows it as seen from the East Lodge, Rousdon, 

 over the Coast Guard Station. C. E. Peek. 



Rousdon Observatory, Lyme Regis, Dorset. 



Family Data. 



A year ago circulars were printed and cards issued with a 

 view to the formation of a collection of simple measurements on 

 parents and children, which would be of service in testing 

 theories of heredity. In particular, such problems as are dealt 

 with by me in a memoir on regression, heredity, and panmixia 

 (printed in the Phii. Trans, of the current year), which treats 

 of biparental inheritance, require statistics far more numerous 

 than have been hitherto available. The measurements are of a 

 simple character, involving but little elaboration, and all that is 

 required is a willing father, mother, and one or more sons or 

 daughters. 



Three thousand cards and circulars were distributed, but 

 experience has shown that general distribution is of little prac- 

 tical value. The cards are readily taken, but rarely returned. 

 The only satisfactory method is to find a willing helper who is 

 sufficiently conscious of the importance of the problems of 

 heredity to distribute and collect himself ten or twelve data 

 cards. 



Up to the present I have obtained measurements on about 700 

 families. I am most anxious to reach at least 1000. May I 

 make an appeal through NATt'RE for such helpers ? I am pre- 

 pared to send full directions and any number of cards to any of 

 your readers who are willing to help. All I would ask is that 



