THE MAKING OF A MICROSCOPE. 



By WILFRED MARK WEBB, F.L.S. 



With Illustrations from Photographs specially taken by Messrs. Lascelles & Co. 



The microscope has come to be used in so many 

 branches of scientific research, and, we may add, of 

 everyday commerce, that it has occurred to us that 

 a short illustrated account of the way in which the 

 instrument is made would be of interest to our readers. 

 Accordingly Messrs. W. Watson & Sons were ap- 

 proached, and they kindly gave permission for their 

 works at High Barnet to be visited, and afforded 

 all the necessary facilities for taking the photo- 

 graphs from which our illustrations have been made. 



The work may well be divided into two parts, and 

 we may consider it under two headings : firstly, the 

 making of the metal stand and fittings ; and secondly, 

 of the optical parts, or, in that slang which the Royal 

 Microscopical Society is content to use, "brass" and 

 " glass." Figure 246 shows a general view of the 

 machine shop where the metal parts of microscopes, 

 and also of telescopes, field glasses, and so on, 

 are got into shape. It may be said at once 

 that the rough castings (see Figure 250) are 

 not made at the works. The first process 

 through which the foot, for instance, of a microscope 

 is put is grinding, by which the fiat surfaces are 

 made true, as shown in Figure 247. 



The surfaces which cannot be ground are milled 



that is to say, cleaned up in the machine provided 

 with a revolving wheel furnished with a number of 

 cutting teeth (see Figure 249). 



At the back of the machine shop is a room con- 

 taining the forges and also an interesting machine, 

 shown in Figure 248, which gives a very great 

 mechanical advantage, by means of which the brass 

 tubing used for the bodies of microscopes and other 

 instruments is brought to the exact size required ; 

 the tubing is pulled over a metal core of the exact 

 diameter which is required through a hole in an iron 

 plate which corresponds with the outside measure. 

 It may be added that the tubing is made smaller 

 during the operation and is lengthened considerably, 

 while its hardness is very greatly increased. 



Turning to other parts of the microscope stand it 

 is not necessary to describe the turning and screw- 

 cutting in connection with various fittings ; but to 

 give some idea of the accuracy which has to be 

 obtained it may be mentioned that in the case of 

 the screw-threads in telescopes which are made for 

 Government an error of only ± -0005 of an inch is 

 allowable. In a smaller shop special work is done. 

 For instance, it is found necessary, when making the 

 surfaces true which are to be moved by the fine 

 adjustment of the microscope, that this should be 

 done on a planing machine worked by hand, as 

 shown in Figure 251. The processes of blackening 

 and bronzing differ but little, if at all, from those in 

 use in the case of other metal work, and we may 

 leave the making of the stand on one side for a 

 moment to consider the very important question of 

 lens grinding. 



The special optical glass which is imported for 

 the purpose of lens-making is received in small slabs, 

 of which half a dozen are shown in Figure 252. 

 These are slit up into pieces, which are of the 

 required thickness and size, by means of an apparatus 

 similar to that used for slicing precious and 

 ornamental stones. It is, for all practical purposes, 

 a circular saw in the form of a revolving metal 

 disc, the teeth of which consist of diamond dust 

 hammered into its edge. The machine and discs 

 used are represented in Figure 253, where a block of 

 glass partly sawn through is seen in position. 



The next operation is to trim up the square pieces 

 of glass so as to make them approximately circular 

 by clipping them with shears. They are then 

 ground or roughed into shape (see Figure 254), and 

 afterwards taken to the glass shop, a view in which 

 is seen in Figure 261. Here the larger lenses for 

 eyepieces and low-power objectives are polished and 

 made true, and we illustrate the details of the 

 process in Figure 255, where blocks of lenses are 

 seen, showing how convex, concave, and plane 

 surfaces are produced. The polishers are fastened 

 to a crank which causes them to rotate with the 

 particular motion required. It should be mentioned 

 that fine rouge is used at this stage. 



Small microscope lenses are fastened on to a block 

 in the same way and held by the hand into a 

 revolving cup, as seen in Figure 256, while very 

 small ones for high-power objectives are fixed singly 

 to handles and polished individually. A pair of 

 holders may be seen lying on the table in the figure 

 just mentioned. 



From time to time as the work proceeds the lenses 

 are tested with a proof plate, the surface of which, 

 in the case of convex lenses, of course, will be con- 

 cave, and vice versa. The method of applying this 

 is seen in Figure 257 in the case of a good-sized 

 lens, and the proof that the latter is accurately 

 ground is shown when it is brought into contact 

 with the plate by the formation of a perfect series 

 of Newton's rings. After the lens is polished its 

 edges have to be ground, and we illustrate this in 

 Figures 258 and 259 in the case of a large lens, and 

 also that of one which is to be used in the making of 

 a one-twelfth objective. Putting together one of the 

 latter is,of course, a most delicate process and requires 

 great skill. The flint and crown glass constituents 

 of the lenses have first of all, as in other cases, to 

 be cemented together and then the whole series has 

 to be mounted in the metal fittings and adjusted. 

 This is done at Messrs. Watson & Sons' works by 

 means of measurements, with the result that very 

 few of the finished objectives, which are turned out 

 in considerable numbers, do not pass the test the 

 first time. 



Now we may consider that we have all the parts of 



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