1897J MICROSCOPICAL JOURNAL. 335 



cause the spherical aberration to be increased four-fold. 

 Now as the difference between the aberrations arising 

 from the spherical and hyperbolic curves is for the pur- 

 poses under consideration insignificant, the above is a re- 

 markable instance of straining out a gnat and swallow- 

 ing a camel (Fig. 2). 



The next important ste[) is the application of a field 

 lens to the eye-piece by Monconys and Hooke. Mon- 

 conys' microscope was made in 1660, an account of it 

 being published in liU'u). The application of a field lens 

 was ahso claimed by Hooke, who in 1665 published an 

 account of his microscope. Hooke's microscope is a 

 very important one, for in it we find several new feat- 

 ures, such as the inclination of the body, a screw focus- 

 sing adjustment, a movable object-holder, and an entirely 

 novel illuminating apparatus. In Fig. 3 we see a heavy 

 circular foot, p, with an upright post, />, fixed excentri- 

 cally to it. The limb which holds the body of the micro- 

 scope is attached to the post by a sliding ring, o, and 

 screw clamp. Tlie limb is also jointed by a ball and 

 socket. x\t the other end of the limb is a ring, d, into 

 which the body screws with a coarse thread. This forms 

 the fine adjustment. The body, a, was fitted with four 

 draw tubes. This form of mounting for the body of a 

 microscope I call the "telescoi)e mount," for the micro- 

 scope is pointed at the object precisely in the same man- 

 ner as a telescope would be. There is an ingenious 

 object-holder, r, consisting of a s})ike caj)able of rotation, 

 held by a short pillar attached excentrically to a rotating 

 disc. This disc is held in position by a link and butter- 

 tly nut, q; obviously, therefore, the object can be placed 

 in any desired position by these combined movements. 



The lamp also was attached to a separate u{>right sup- 

 port by a ring and screw nut, very much in the same 

 way as it is fixed at the present time. There was an 

 rengaver's globe, /i, filled with water for a primary con- 



