20 ANNUAL OF SCIENTIFIC DISCOVERY. 



science, invented the machine, and some time afterwards presented 

 it to the Microscopial Society, by whom it was exhibited at the great 

 International gathering. Suppose that a metal bar is suspended ver- 

 tically, by a fulcrum or point exactly in the middle ; if the bar is 

 swung to and fro, the top will describe a curve exactly like, in size 

 and form, that described by the lower end, but opposite in direction. 

 If the lower end is twice as far distant from the fulcrum as the upper, 

 and if the bar be swung to and fro, the lower end will describe a 

 curve or arc just twice as long as that described by the upper, though 

 similar in shape. If, on the other hand, the lower end of the bar be 

 nearer to the fulcrum than the upper ; and if the ratio of distances be 

 (say) ten to one, then the upper end will describe an arc ten times 

 as large as the lower, though of course reversed in direction. And 

 so on in any other ratio. Xow, let there be a blunt tracer at one 

 end of the bar, and a pencil at the other ; if we write, or draw, or 

 trace any figure with the tracer, the pencil may be made to copy the 

 figure on a piece of paper, enlarged if the tracer be nearer to the 

 fulcrum than the pencil, diminished if otherwise. Here we have the 

 first germ of Mr. Peters's micrograph ; a writing in moderately-sized 

 characters, reproduced in smaller dimensions by this kind of panta- 

 graph. In the first machine which he made, the fulcrum was a hun- 

 dred and twenty-five times nearer to one end of the bar than to the 

 other ; and the pencil-copy was to the tracing in the ratio of one to 

 125 in size. But notable as was this power of diminution, Mr. Pe- 

 ters hit upon an expedient that enabled him to eclipse it in an aston- 

 ishino- decree . Instead of causing the short arm of his bar or lever 



^j ^j ^j 



to carry a pencil or graver, he caused it to move the long arm of an- 

 other but much smaller lever ; tnus obtaining the product of the two 

 diminutions multiplied into each other, instead of the diminution due 

 to a simple lever. In his large lever, he made the fulcrum 125 times 

 nearer to the short than to the long end ; in his smaller, the ratio 

 was 50 to one ; and as the short arm of the first acted upon the long 

 arm of the second, tin- two ratios were multiplied, insomuch that the 

 copy-writing was li^'.'ii) times smaller than the original tracing. Sup- 

 pose, for example, that the tracer ruled parallel lines one-tenth of an 

 inch apart ; then the pencil would rule lines 1-62, 500th of an inch 

 apart ; and any writing, drawing, or device would be reduced in sim- 

 ilar ratio. The next achievement of Mr. Peters was so to construct 

 the exquisite details of his machine that he could vary the power of 

 diminution at pleasure, from a ratio of one to 110 up to a ratio of 

 one to 0250. Considering that no kind of pencil could draw such 

 minutely approximate lines on paper, lie employed diamond to scratch 

 on glass. The bits of diamond called " turned points "are found 

 better for this purpose than " splinters." The long end of the lever, 

 which is downwards, carries a tracer, with which any design or writ- 

 ing is traced. The upper end carries a small piece of glass, careful- 

 ly adjusted ; over the glass is mounted a diamond pointing down- 

 wards, which remains stationary while the glass moves under it. 

 Delicate mechanism is connected with the diamond, .by means of 

 which it may be raised or lowered, and also pressed with greater or 

 less force upon the. ^la.-.s ; and so effective are these contrivances, 

 that the thick and thin strokes of ordinary writing can be faithfully 

 transferred to the minute copy on glass. 



