1 1 



sufficient size to admit of a liberal reduction when the drawing 

 is photographed on metal preparatory to etching. Thus, ii it 

 is desired to publish an illustration having a" magnification of 

 50Q diameters, it is advisable to produce a blue sketch at from 

 1,000 to 2,000 diameters. This is easily accomplished with the 

 apparatus that has been described. By placing the prism reflect- 

 or at a considerable horizontal distance from the eye-piece of the 

 microscope, say one foot, and lowering the right hand leg-of- 

 mutton table sufficiently, magnifications of liberal dimensions are 

 easily secured. Needless to say the production of a large coarse 

 drawing is an easier matter than the production of the same 

 drawing on a smaller scale, so that the operation is not only bet- 

 ter, but considerably easier if carried out in the manner describ- 

 ed. It is unnecessary to go into the details of converting the blue 

 sketch into a pen and ink drawing. These present no peculiari- 

 ties. It ought perhaps to be mentioned that the object of using 

 the blue color is to avoid trouble through the alterations that 

 may be necessary in finishing the drawing. Any light blue lines 

 which are left on the enameled board need not be removed, as 

 they do not affect the sensitive photographic film sufficiently to 

 cause any intonvenience in the production of an etched block. 

 The black tissue paper mentioned is produced by inking ordin- 

 ary tissue. The ordinary blue carbon paper gives too dark a 

 blue to meet the requirements. The blackened tissue is rubbed 

 on one side with dry Prussian blue powder. This gives a light- 

 blue tracing. 



At an eariier stage it has been mentioned that all the acces- 

 sories in connection with the microscope are painted black. In 

 addition to this precaution, arrangements are made such that 

 the room itself can be darkened, in fact, converted into a photo- 

 graphic dark-room at will. This object is secured by having all 

 the window blind connections light-tight. The oblong aperture, ' 

 about five inches by eight inches, through which the micro- 

 scope receives its light is screened by means of several thick- 

 nesses of flexible black cloth made into the form of a sleeve. 

 This cloth sleeve attached around the perimeter of the open- 

 ing, is notched above so that it surrounds the microscope 

 just beneath the stage and buttons onto one of the screws at 

 the back of the microscope. No light reaches the eye ex- 

 cept that which comes through the instrument. If, now, the 

 slide in front of the large glazed aperture be closed and the room 

 be darkened, the operator sits in absolute darkness. Any one 

 who has had experience with a photographic dark-room, must 

 have observed how after a period of fronl five to ten minutes 

 therein the eye becomes accustomed to the darkness of the room 



