86 



HARDWICKE'S SCIENCE-GOSSIP. 



The body was fixed oil a stand in a horizontal posi- 

 tion, and was provided with a stage for the objects. 

 The body had a coarse adjustment by means of a 

 rack and pinion moving the framework supporting 

 the body, and a fine adjustment effected by means of 

 a thread on the end of the body. 



In 1702, Jean Zalm published at Nuremberg his 

 "Oculus artificialis Teleodioptricus," in which he 

 describes several compound microscopes, and gives 

 a figure of the microscope of Francis Grindelius, 

 of which fig. 43 is a copy. It will be seen that 

 the optical part consisted of six plano-convex lenses, 

 and like Hooke's, could only be used for cpaque 

 objects. Glass was not the only material used for 

 the purpose of forming lenses. Mr. Stephen Gray, 

 in No. 221 of the "Philosophical Transactions," 

 describes the construction of his water microscopes: 

 these were made of thin brass, about r V of an iuch 

 in thickness, in which a minute hole was drilled ; a 

 drop of water was; taken up with a pin and placed 

 in the aperture ; the water retained its convex form, 

 and, of course, magniGed any object placed in front 

 of it. This gentleman also made lenses of minute 

 drops of isinglass dissolved in hot water. The in- 

 vestigations made by Leeuwenhoek with his simple 

 microscopes was in great measure the cause of the 

 neglect of the compound form, and many years 

 elapsed before much attention was paid to these 

 arrangements. The superior definition of the 

 simple microscope compared with the hazy outline 

 of the image as shown by the compound instrument 

 readily accounts for the preference ; the compound 

 microscope was also cumbrous and unmanageable. 



In 1738 Lieberkuhn invented the solar micro- 

 scope, and the little concave reflector, now known 

 by his name. He exhibited his microscope to some 

 of the Fellows of the Royal Society. Mr. Cuff, an 

 English optician, improved Lieberkuhn's solar 

 microscope, by adding a movable reflector, by 

 means of which the instrument became more -avail- 

 able. 



The injected preparations of Lieberkuhn were 

 famed for their beauty, and, like Leeuwenhoek, he 

 provided a microscope for each preparation. The 

 diagram fig. 45 will illustrate the manner of viewing 

 the object. 



The drawing (fig. 47) represents the "Martin's 

 microscope" as improved by Messrs. Cuff & Scarlett. 

 This instrument was introduced in 1750, and very 

 many of them must have been made, as they may 

 now be occasionally seen. 



About this time Benjamin Martin introduced his 

 "Universal Microscope with a Micrometer." This 

 instrument consists of a brass body fixed to an arm, 

 with a ball-and-socket movement, by means of 

 which the body was moved to the right or left ; the 

 stage was made to slip up or down the pillar sup- 

 porting the arm, and was the only means of focus- 

 sing the object. 



We give a figure (46) of a part of the ocular to 

 which the micrometer is fixed, and a diagram showing 

 its arrangement, copied from a "Course of Lectures in 

 Natural and Experimental Philosophy," by Ben- 

 jamin Martin/'Readicg, mdccxliii. In the original 

 drawing the screw is represented as tapering 

 towards the point, but this is no doubt erro- 

 neous. Martin in the same work figures a "Pocket 

 reflecting microscope with micrometer." * This re- 

 sembles in make the non-achromatic toy microscopes 

 of the present day advertised to magnify " 10,000 

 times." It is not quite clear why he calls it a reflect- 

 ing microscope, unless on account of the object 

 being illuminated by reflectors. His diagram repre- 

 sents it as constructed with a bi-convex lens as an 

 objective. Martin was the maker of the very elabo- 

 rate instrument formerly belonging to George HI., 

 and purchased by the Royal Microscopic Society at 

 the sale of the effects of the late Professor Quekett. 

 A full account of this microscope will be found in 

 vol. x. page 31, of the " Transactions of the Royal 

 Microscopic Society." The following is the author's 

 description of the objectives belonging to this in- 

 strument : — " Ten of them range from 4 inches to 

 T V of an inch in focal length. These are also num- 

 bered from 1 to 10, No. 1 being the highest power. 

 In addition to these, in one of the drawers are three 

 higher powers, which appear to have been an after- 

 thought. The focal lengths of these are marked 

 respectively T Vth, ^'ath, ^th. There are also four 

 powers marked T Vth, T Vth, ^th, and ^th, and 

 numbered from 1 to 4. These last cannot be used 

 with the compound body, but as single lenses only, 

 and for their employment a small arm is provided, 

 which fits on the back of the instrument, which can 

 be turned round, and brought into proper position 

 for use. The ^Vth is the smallest ground lens ; I 

 have even seen it as scarcely larger than the aperture 

 of its setting. There are also nine Lieberkuhns of 

 various sizes, for viewing opaque objects, belonging 

 to the instrument." 



The following are the results obtained by testing 

 the Ts-t.li, aVth, and ^th, a scale Morpho Menelavs 

 being used as a test object : — 



The T V indistinct traces of lines, very ill defined. 



The 5 V lined distinctly, but the definition any- 

 thing but sharp. 



The 3V lined distinctly, but still without good 

 definition; the amplification in all these cases being 

 far beyond that which is necessary for bringing out 

 the lines sharply with the present object-glasses of 

 much lower power. 



The very fine-lined scales of Lepisina were tried 

 with the 30th ; " very faint traces, amounting to a 

 mere suspicion of lines, was all it would exhibit." 

 This instrument has the following inscription 



* The price of these instruments was, with micrometer, 

 21s. ; without, 10s. <3d. 



