528 SUMMARY OF CURUKNT RESEARCHES RELATING TO 



Mr. R. Hitchcock suggests that instead of making a camcra-lncida 

 drawing, a negative should be taken from the object, and a blue 

 print made on the ferro-jirussiate paper. The drawing may then be 

 traced from that on the tracing-paper, which would doubtless be a 

 better plan for those who cannot use the camera well ; but the fol- 

 lowing plan is even better. Coat very thin and transparent paper 

 with the forro-prussiate solution, and print from the negative upon 

 that. Then draw the outlines and necessary details on the print with 

 indian ink. Having done this, bleach out the blue picture with very 

 dilute ammonia, which will leave the paper white, witli the black ink 

 lines intact. Should there he a yellowish colour left on the paper, a 

 little weak acid will remove it. After the paper is washed and dried, 

 it may be spread on a flat, heated plate — a flat-iron, for example — and 

 paraffin rubbed over it. This will make the paper transparent (like 

 " wax-paper ") and it can then be attached to a glass plate, as suggested 

 by Mr. Vorce. 



Value of Photo-micrograplis.* — Mr. T. Charters White calls 

 attention to some photographs of young tench in their eggs, as show- 

 ing that the sensitive film (or " retina of science ") possesses a power of 

 discriminating greater than that possessed by the human retina, a 

 structure quite invisible under the Microscope may become distinctly 

 visible in the photograph. When seen under the Microscoj^e the jelly- 

 like envelopes were of a clear and structureless character. What, 

 however, was clear and gelatinized under the Microscope, was in the 

 photograph shown to be pierced by innumerable tubes which passed 

 through the egg-cases in parallel lines. 



Parallel Rays in Photo-micrography.t — Mr. W. Pumphrey calls 

 attention to the great advantage obtained by the use of parallel rays, 

 obtained by causing the light to traverse two apertures, placed 

 Ih in. from each other, interposed between the lamp and the object. 

 By this means the intervention of a condensing lens is dispensed with, 

 and a much finer definition obtained. 



Small Negatives— Robinson's Miniature Microscopic Camera.— 

 Dr. Eoux makes negatives about the size of a sixpence, which bear 

 enlarging to the ordinary lantern size of transparencies. These 

 negatives go far to support what is not generally allowed — that better 

 negatives of bacteria and very minute objects can be produced without 

 the eye-piece, by obtaining more perfect small negatives, than by 

 original large direct negatives. There is, of course, the additional 

 trouble of copying and enlarging ; but this must not be a hindrance 

 when seeking for the best work. 



The plan adopted by Dr. Eoux, intended to meet rapid laboratory 

 work, is to fix a small camera or cell to the eye-piece end of the 

 Microscope, containing a little gelatino-bromide plate, the position of 

 the focus and the image having been previously determined by 

 placing a piece of plain glass in the slide, and on its upper surface a 



* Photogr. News, xxix. (1885") pp. 179-^0 (2 figs.), 

 t Midi. Natural., viii. (1885) p. 113. 



