236 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Oct., 1904. 



bed of plate glass supported on levelling screws, along 

 which is drawn at constant speed a piece of glass 

 covered with velvet on its under side and carrying the 

 plates to be coated. The trough that holds the emul- 

 sion is made of platinoid, it is surrounded with a large 

 hot-water bath, and to pass the emulsion to the plates 

 it has a slit below, that is made with great accuracy 

 and adjustable like a spectroscope slit. The trough is 

 7 cm. high and i cm. wide. I should have thought 

 that the alteration in level of the emulsion during the 

 coating would have caused a variation in the thickness 

 of the layer deposited, but there appears to be no 

 mention of this. As a constant light, the authors 

 employ a small area screened off from an acetylene 

 flame. 'J'o graduate the light, a rotating disc with 

 apertures in it of the ordinary kind is used, but it was 

 made with special accuracy and calibrated before use. 

 Much convenience and advantage results from enclosing 

 the disc in a case with an opening and grooves on one 

 side to take the slide that contains the plate, and a 

 camera-like extension on the other containing a flap- 

 shutter for starting and closing the exposure, cells for 

 colour screens, and a diaphragm. It need not be used 

 in a dark room. For developing the plates, which are 

 one inch or an inch and a half wide, a thermostat con- 

 taining about 10 gallons of water is used, with a 

 stirrer, and a regulator of the ordinary Reichart type, 

 the developer being contained in vertical glass tubes. 

 During development the plates are rotated in the tubes, 

 being suspended from vertical spindles for this purpose. 

 The authors appear to find that this movement is better 

 than a rocking movement with the plate horizontal, but 

 still not perfect. I should have thought that this 

 method would give a difference according to whether 

 the end of the plate with the longest exposure was 

 placed uppermost or otherwise, because at this end 

 there must be the greatest change in the developer, 

 and the vertical mixing effect produced by the regular 

 rotation of the plate on a vertical axis in a tubular 

 vessel must surely be very small. For measuring the 

 opacities the authors use a Hufner spcctro-photometer, 

 but with several nn)dilications to fit it for this particu- 

 lar work. I may be mistaken, but I cannot find from 

 the description that the difficulty of the scattered light 

 is met in any way. It is easy to measure something, 

 and with considerable accuracy, but if the something 

 measured is indefinite the results cannot be very 

 valuable. It is better to sacrifice a little accuracy if 

 necessary for the sake of knowing exactly what is 

 being dealt with. Perhaps the authors have taken 

 more precautions than are obvious for their descrip- 

 tion. Regarding the apparatus as a whole, it appears 

 to me that it presents many points of advantage that 

 future workers will profit by, but I am convinced that 

 there are many matters that need investigation before 

 the results obtained in working with it can be accepted 

 without qualification. I have sought only to give a 

 general idea of the apparatus ; those interested will, of 

 course, refer to the original paper. 



A iXc/ta-nlis/'s Camera. — The possibility of getting 

 good typical photographs of living things has been 

 amply demonstrated during the la"st few years, and 

 many photogra|)hers ha\e dcx'oted themselves to this 

 kind_of work. That results of the first quality can be 

 obtained with an ordinary camera when supplemented 

 by home-made contrivances, has been shown by the 

 brothers Kearton ; but the methods which thev follow 

 are possible for only a very few and appreciated by 

 still fewer. Hence the demand for special facilities. 

 One of the most recent cameras that has been devised 



to meet this demand is the " Birdland " camera de- 

 signed by Mr. Oliver G. Pike and constructed by 

 JNIessrs. Sanders and Crowhurst. It is a hand camera, 

 for Mr. Pike's method of work is to follow the bird he 

 wishes to photograph, focussing it meanwhile with one 

 hand upon the full-size reflex finder, and to release the 

 shutter with the other hand as soon as the bird is in 

 the desired position. The well-known Anschutz focal 

 plane shutter is made to form a part of the camera, 

 and an especial part of the apparatus is the connection 

 of this with the mirror of the finder so that when the 

 release is actuated the mirror moves out of the way 

 immediately before the opening in the blind passes 

 across the plate. The whole movement follows so 

 quickly on the touch of the trigger that there is no 

 sensible interval, nor is there any jar or noticeable 

 noise. The camera has many conveniences, the chief 

 of which are a mirror in the finder hood, so that the 

 image can be observed and focussed with the camera 

 level with the eye, and the possibility of opening the 

 front and drawing the lens forward, as shown in the 

 figure, to allow of one combination of the doublet, or 

 a lens of greater focal length, being used. The sensi- 



tive material is carried in double backs, changing 

 boxes, or roller slides. A camera of this kind is, of 

 course, eminently suitable for almost any work in 

 which a moving object has to be photographed at a 

 critical moment, and that this particular instrument 

 serxes the purpose well is abundantly demonstrated by 

 the photographs obtained by its aid by Mr. Pike him- 

 self and by Mr. F. Martin Duncan. A small selection 

 of these is reproduced in the pamphlet describing the 

 camera, which can be obtained on application to the 

 makers. 



The Scintilloscope. 



One of the small defects of the cleverly-devised instru- 

 ments for displaying the scintillations which are produced by 

 the bombardment of radium is. that the speck of radium is 

 placed on a tiny pointer, which is between the spectator's eye 

 and the screen of pitchblende or other material that is bom- 

 barded. Consequently, the pointer partly obscures the effects. 

 In a little instrument sent to us, and called 

 (dew's " Scintilloscope." the defect is reme- 

 died in an ingenious way. The instrument 

 is in two parts, one part of which is the usual 

 magnifying lens. The other part, detach- 

 able, is a double screen. The upper part of 

 the screen is a thin plate of pitchblende polo- 

 nium, or thorium, all of which are extremely 

 sensitive to the impact of the "alpha" 

 rays that proceed from a radio-active material. 

 The lower or underneath part of the screen consists of a plate 

 coated with some such material. The alpha rays strike 

 upward, and produce scintillations of great brilliancy on the 

 pitchblende or polonium above. The instrument is fitted with 

 one, two, or three screens, and the difference in the effects 

 produced is very interesting. 



