6 INTRODUCTION. 



and J in. focus, using the 6 in. or continental tube length (Swift, 

 Beck, &c.). Oculars Nos. 2 and 4 with objectives a s and D of Zeiss. 

 Ocular No. 3 with objectives Nos. 2 and 6 of Leitz. 



The last-named maker supplies his No. IT b stand (Fia. 1) with 

 cylinder diaphragms carried in a sub-stage adjusted by a lateral screw 

 together with the ocular and objectives mentioned, and a double 

 nose-piece, for 6 5s. An iris diaphragm can be substituted for the 

 cylinder form for 10s. By the subsequent addition of a Homog. immersion 

 objective and a condenser, this instrument will fulfil all the requirements 

 of the student in pathology. As far as my experience goes it is 

 simple, efficient, and well made. 



Method to be followed in focussing the microscope. Always 

 see that there is sufficient clearance beneath the objective before 

 placing an object upon the stage. Adjust the mirror so that the 

 field is well and uniformly illuminated. Use the plane mirror with the 

 low power and the concave one with the high power, and keep the centre 

 of the mirror in 'the optical axis of the microscope. Employ a small 

 aperture of the diaphragm with the high power. Place the slide in position 

 on the stage with the left hand, and clamp it there with the right 

 hand clip. With the low power bring the object sharply into view 

 by means of the coarse adjustment. To use the high power immedi- 

 ately afterwards, revolve the nose-piece ; the objective will come into 

 place above but close to its position of focus. Move the slide to 

 and fro on the stage with the left hand, and use the coarse adjustment 

 until the moving object is perceptible ; let the object rest, and complete 

 the operation with the fine adjustment. The high power is usually 

 so adjusted on the nose-piece that it takes up a position which only 

 necessitates a turn of the fine adjustment to bring the object into 

 focus. 



Cape of the microscope. Keep the objectives screwed to the 

 nose-piece. 



To detect the position of dirt. If denned specks, &c., are seen in 

 the field they are on the eye-piece and will move when the latter is 

 turned. Raise the eye-piece, partially unscrew the upper (e} r e-) lens, if 

 the specks move with the lens, the latter must be cleaned, if they 

 remain stationary clean the lower (field-) lens. 



If objects focussed on the stage appear dim, the objective is soiled. 

 Remove it and examine its front lens with an inverted eye-piece held 

 close to it. To clean lenses gently dust them with a clean piece of 

 wash leather kept for the purpose. If this fails moisten with water, 



