252 Transactions of the 



damaging the negative. I have found that no other light answers 

 so well as sunlight for microscopic photographs ; artificial light 

 is a delusion, with perhaps the exception of the electric light, 

 hut the trouble and expense of this precludes its employment in 

 a private house, for at least fifty cells would be required. Mag- 

 nesium ribbon gives an impression, but I have always found 

 it impossible to get a good focus ; perhaps if it could be 

 arranged so as to give a steadier light it might answer ; Dr. 

 Woodward appears to have succeeded with it. As before men- 

 tioned, condensers, ground glass, &c., are unnecessary, at least 

 for the |-inch and lower powers ; the ordinary concave mirror 

 attached to every microscope being all that is requisite ; but even 

 with the lowest power this mirror should be used, as with the flat 

 one the image of the spots of dust and other extraneous objects 

 comes out with painful distinctness. If the object to be copied is 

 an ordinary microscopic preparation, no especial precautions are 

 necessary ; but in cases where fresh tissue examined in fluid is the 

 subject, it is better to paint the edge of the thin glass cover tempo- 

 rarily with gold size to prevent evaporation ; this is easily rubbed 

 ofi:' after use. If the subject is not very pervious to Hght, a good 

 plan is to paint the surface of the slide round it with Indian ink, in 

 fact, to stop out all light except that which passes through the 

 object. Hitherto I have spoken only of taking the negative ; I now 

 come to the consideration of the best way of printing. It is gene- 

 rally remarked that the former may have all the finest definition 

 that can be desired, but that in the latter the greater part of this 

 distinctness is lost. ISTow by the process which I am about to 

 describe, prints can be obtained absolutely equal in point of defini- 

 tion Avith the negatives, and three or four times tlieir size ; for 

 instance, if a negative has been taken by the |th objective, doubling 

 it will shoN\- all that is seen (being in focus) by that glass with the 

 A eye-piece ; trebhng its size will show the same as with B eye- 

 piece, and so on ; but if the negative has been taken by the l|-inch 

 objective, magnifying it six times will not make it show what is to 

 be seen by the §rds objective, so that by this process one cannot 

 substitute a lower for a higher objective, but simply compensate for 

 the absence of the different eye-pieces in taking the negative. The 

 method' consists simply in printing on a collodion film instead of on 

 paper. Moitessier is the only writer on microscopic photography, 

 that I am aware of, who mentions it. The same apparatus is used 

 for printing in this manner as for the preceding process ; the 

 microscope being removed, a short focus photograpliic lens is 

 screwed into its place ; the front frame is then fixed at such a 

 distance from the focussing frame as to give a magnifying power of 

 say three diameters. Now another piece of apparatus comes into 

 use ; this is a wooden frame to carry the negative ; it works in a 



