1885.] 



MICROSCOPICAL JOURNAL. 



43 



have already used it a number of 

 years for silvering prisms and other 

 articles for mv scientific researches. 



' The preparations being opaque, 

 I naturallv have employed the verti- 

 cal illuminator for lighting them. 

 The photograph w^as made v^^ith a 

 y'^-inch homogeneous objective of 

 Zeiss, with a magnification of i,ooo 

 diameters, and the picture afterward 

 enlarged to 3,000, which is not too 

 much for the most delicate details. 



' The photograph is very difhcult 

 to obtain, first because in the light 

 employed the valve appears green 

 and the details are shown with diffi- 

 culty ; secondly, because details so fine 

 disappear with the slightest move- 

 ment of the apparatus. 



' The first proofs, obtained with a 

 large microscope of Messrs. Powell 

 & Lealand, which is however a model 

 of admirable precision, were very de- 

 fective. I did not obtain better ones 

 until I had replaced the mechanical 

 moving stage bj' a rigid stage. Dr. 

 Maddox has suggested the idea that 

 the difficulty of obtaining these proofs 

 may be due to dilatation of the cover- 

 glass during the exposure. 



' As source of light I employ ex- 

 clusively, for my microscopical re- 

 searches, the incandescent electric 

 lamp, and that since the month of 

 November, 1881, when I applied it 

 to the microscope. My electric in- 

 stallation is very complicated, for it 

 lights not only my microscope, but 

 also a portion of the house, and es- 

 pecially my cabinet of work, which 

 is very large and occupies all the sec- 

 ond and third floors of my house. 

 The light is produced by an Otto gas 

 engine of i|^ horse-power ; it actuates 

 a Siemens dynamo machine which 

 charges large accumulators. 



• I use Swan lamps exclusively. I 

 have tried all the electric lamps possi- 

 ble and have finally concluded that 

 the Swan are the only good ones, for 

 they alone permit one to obtain a 

 white light without injury. It is well 

 known that the blue and violet rays 

 which exist in abundance in white 



light permit the resolution of diffi- 

 cult details. This is one of the ad- 

 vantages which I proclaimed in 1882 

 in favor of the electric light. 



' At times 1 use the small lamp for 

 the microscope (micro-lamp a) of 

 Swan, but generally I give prefer- 

 ence to the lamp of six volts, a very 

 perfect form of lamp which Mr. 

 Swan had the kindness to make for 

 me in 18S2. This lamp gives white 

 light with three accumulators, but one 

 can operate it veiy well with three 

 Bunsen elements. 



' As concerns the photographic ap- 

 paratus, the simplest is the best. I 

 first commenced with an outfit like 

 that of my friend Dr. Woodward, 

 that is to say, I devoted an entire 

 perfectly dark room to the photo- 

 graphic apparatus, where the micro- 

 scope could receive at will light from 

 electricity, the oxyhydric light, or 

 from the sun with the aid of a helio- 

 stat, but I soon found that it was not 

 what I wanted and that, save in very 

 rare cases, photography should be, 

 for the micrographer, not an end but 

 a means ; that is to say, that one 

 should employ photography not for 

 the pleasure of producing pictures, 

 but to replace the camera lucida and 

 the pencil, in case the latter could not 

 render excessively delicate details 

 sufficiently well, or when it is desira- 

 ble to show a certain and undeniable 

 proof in support of a newly asserted 

 or controverted fact. 



' For all that the installation of 

 Woodward is not what is required. 

 One is not certain when an object with 

 very fine details is taken from the 

 microscope that it can be placed under 

 another microscope in the same con- 

 ditions of illumination. In any case 

 this cannot be done without great loss 

 of time. 



' My second apparatus consisted of 

 a camera as perfect as possible (a 

 model of Watson's), quarter-plate 

 size, carrying in place of the photo- 

 graphic objective a tube containing a 

 Tolles amplifier. This camera was 

 mounted on an elevated inclined plane , 



