100 On graduating Glass Tubes. 



a 



with 4 screw-nuts, passing through a cut portion of the plate, 

 a quarter of* an inch long, so as to allow a certain advancement 

 or withdrawal of the plate at pleasure. C and D are two si- 

 milar plates, placed at the other end of the wooden board, C 

 having the same amount of motion as B, and being precisely 

 similar in every respect. D is a brass plate of the same di- 



Scale six-tenths of an inch to the foot. 

 - - - - 5 feet 6 inches. - - - 



<-Brass 1 foot 9 inches. -> 



T\ 

 Hali k v 

 na . tural I d — W 



size. 



3 feet. 



Half 

 natural 



size. 



mensions as B and C, but the screws go through a hole of the 

 same size as themselves into the wood. It is cut, at intervals 

 of five millimetres, into notches, every alternate one being one- 

 twentieth and one-tenth of an inch deep. The instrument is 

 provided with a wooden rod, 3 feet long, 1 inch broad, and 

 half an inch thick, E. This is provided with two steel points, 

 placed by screws at half an inch from either end. One of these, 

 F, is in the form of a knife, the other, G, of a bradawl. 

 The instrument is furnished with a screw-driver, that these 

 may be removed at pleasure. 



When a tube is to be graduated, it is covered with a thin 

 layer of melted wax and turpentine, by means of a camel's- 

 hair pencil, and is placed in the groove between C and D, 

 which are then screwed down in their places, so as to retain 

 the tube firmly in its position. A standard tube, previously 

 mathematically divided into millimetres (the most convenient 

 division), is now placed in the groove under B, which is then 

 screwed upon it. The rod E is now used, the pointed steel 

 G being put in one of the millimetre marks on the standard, 

 tube ; the knife-formed steel F is now upon the waxed tube, 

 and is made to make a mark upon it, the length of which is 

 regulated by the distance between the edges of C and D. 

 The pointed steel is now removed back one millimetre on the 

 standard tube, and the corresponding mark made on the waxed 

 one; and thus we proceed until the whole of the waxed tube 



