234 



NATURE 



[July 9 1903 



phosphorescence emitted did nol diminish, but a thm layer 

 of pure water entirely arrested the n radiations. These 

 radiations may be concentrated by a quartz lens, but are 

 regularly reflected by a polished glass surface, whilst an 

 unpolished glass surface diffuses them. 



The Spectra of Metals and Gases at High Tempera- 

 tures. — In No. 25, vol. xxxviii., of the Proceedings of the 

 American Academy of Arts and Sciences, Prof. J. Trow- 

 bridge gives the details and results of an exhaustive series 

 of experiments on the spectral phenomena observed when 

 gases and metals are together subjected to high tempera- 

 tures. Employing a large variety of conditions as to the 

 temperature employed, the size of the capillary tubes and 

 the materials from which they are made, and the distance 

 and material of the poles, Prof. Trowbridge arrives at 

 several interesting conclusions, all of which tend to show 

 that in many cases the lines obtained are possibly due to 

 products of the interactions between the gas, the poles, and 

 the containing tube, which take place at high tempera- 

 tures, rather than to the elements themselves. For instance, 

 the metallic lines obtained from terminals placed icm. 

 apart in rarefied air, or hydrogen, were reversed, the 

 reversal coinciding in position with the line obtained in 

 ordinary air, but the line was much broadened on the least 

 refrangible side. The author suggests that this indicates 

 the presence of a gaseous product, probably due to the 

 oxidation or hydration of the poles. Again, when highly 

 heated and rarefied hydrogen, or air, was passed through 

 a tube of amorphous silicon or glass, broad bands, co- 

 inciding with the fainter silicon lines obtained under 

 ordinary conditions, were produced, and Prof. Trowbridge 

 believes that in the case of highly refractive metals, such 

 as silicon, these bands are not really due to the metals 

 themselves, but to the interaction between the metals and 

 gases present. 



The experiments showed that iron lines did not appear 

 under what seemed to be favourable conditions, whilst 

 aluminium lines did appear under these conditions. For 

 this reason the author enters a caveat as to the care it is 

 necessary to exercise when classifying stars solely from 

 the variations in the appearances of their respective spectra. 



Zenith-telescope Results. — In vol. ii. part 

 i. of the Publications of the University of 

 Pennsylvania (Series in Astronomy), Mr. C. L. 

 Doolittle, director of the Flower Observatory, 

 gives the results obtained from the observations 

 made with the zenith-telescope during the 

 period September 6, 1898, to August 30, 1901. 

 After describing the corrections applied to the 

 observed values, the report gives full details 

 of each observation and its corrections, and 

 then gives the values of the "aberration con- 

 stant determined during 1898-1899 and 

 1900-June, 1901, as 2o"-540±o"-oio3 and 

 2o"-56i +o"-oo85 respectively. A curve and a 

 set of tables, showing the variation of lati- 

 tude at Philadelphia from October i, 1896, to 

 August 30, 1901, are also included in the 

 report. 



it make a round hole to fit the eye-piece of the microscope. 

 Glue this to the camera front. 



In use the microscope is focused on object for distinct 

 vision for a normal eye. If the experimenter be long- or 

 short-sighted, then he must use apt)r(ipriate spectacles. 



The light issuing from the eye-piece is thus rendered 

 parallel, and if the camera be placed on the top of the eye- 

 piece an image of the object will be in focus on the sensitive 

 film. Of course, the optical axes of the camera and micro- 

 scope must be parts of the same straight line, and the card 

 glued to the camera is to assist the centring. The visual 

 field is the exact area photographed. 



Rhyoli 



PHOTOMICROGRAPHY WITH A BROWNIE 

 CAMr.RA. 



'T'HIS article does not put forth anything new in prin- 

 ciple, but is the explanation of a simple method 

 by which any student can, with little trouble and little 

 expense, produce his own photographs of microscope 

 objects, the idea being to direct attention to the inexpensive- 

 ness of the necessary apparatus. 



The apparatus required includes only a small microscope 

 and a light " fixed-focus " camera, and, of course, the 

 necessaries for developing the negatives. The writer used 

 a microscope of the rigid type generally regarded as little 

 more than a toy, and worth only a very few shillings, and 

 a Brownie Kodak. The instruments need practically no 

 alterations to make them fit for use ; the utmost that need 

 be done is this : — Cut a piece of rather thick cardboard the 

 same size as the front of the camera, and in the centre of 



NO. 



1758, VOL. 68] 



The exposure is made in the usual way, using the camera 

 shutter. In the middle of a fine day exposures of from 

 one to two minutes have been found ample, while in the 

 evening ten or twenty minutes are necessary, using plates 

 of the speed generally known as " Special Rapid." The 

 Brownie camera is made for roll-films, but plates may be 

 used thus : — The camera back is opened and a plate 

 22" X 2^" laid on the frame over which the film is generally 

 passed. On the back of the plate is placed a piece of black 

 paper or thin card, and the back closed. This paper is 

 necessary in order to exclude the light from the little red 

 window, which is not non-actinic. 



After exposure development is proceeded with in the 

 ordinary way, using pyro-soda or any other developer the 

 experimenter may prefer. 



It will be seen from the specimens that the definition is, 

 of course, not of the highest order, but considering the 

 apparatus, one must not expect too much. The photo- 



