750 



SCIENTIFIC RECREATIONS. 



carried in the pocket, and by a very simple process gives (i) the length of 

 any line, straight or curved, traced on a map or plan ; (2) the actual length 

 corresponding to a " graphical " length on maps of the scale of soijiRj- or 

 TUuVo-Q-, or on maps which are multiples of these numbers. 



The instrument consists, of a toothed disc, the circumference of which 

 is dentated exactly in five centimetres. The faces of this disc each carry a 

 system of divisions ; one is divided into four parts, the other into five. The 

 circumference of the disc (5 centimetres) corresponds to the 4 kilometres 

 of the scale of -soinro-, and to 5 kilometres of that of TOTRHJO. The division 

 roof the disc in the former scale measures 100 metres, and is in it the same 

 as A of the other scale. 



The toothed disc moves upon a micro-metric screw, the markings of 



Fig. 877. The campylometer. 



which are 0*0015 of a metre, and a small "rule" or " reglet " carries equal 

 graduations, as the screw representing lengths so follow : 



1. 5, 10, 15, 20 



2. 5, 10, 15, 20 



3. 4, 8, 12, 16 



50 centi. . 

 $o til. . 

 40 kil. . 



. according to metric scale. 



scale 



The micro-metric screw is fixed in a frame so made as to form a kind of 

 indicator or guide at one side. 



To make use of the campylometer, bring the zero of the disc opposite 

 the zero of the rule (reglet), then place the instrument on the map in a 

 perpendicular position ; the point will serve as guide, and move the disc upon 

 the line, whether direct or sinuous, of which you wish to ascertain the length. 



When, this has been done, note the last graduation of the "reglet" 

 beyond which the disc, has stopped, add to the value of this graduation the 



