II. LENGTH. 40 



259. Standard Metre, with rack action to be used as a 

 machine for dividing other metres. 



Geneva Association for Constructing Scientific Instru- 

 ments. 



This instrument may be used both as a comparative indicator, and as a 

 machine for dividing fractions of the metre, for the use of comptrollers of 

 weights and measures. A small marker slides at will, by means of a rack, 

 along the meter. A very simple lock action enables the millimetric displace- 

 ments of the indicator to be registered without any other divisional check. 



2 GO. A 6-foot Measuring Rod, for uneven ground, for 

 engineering and scientific purposes. Designed by Edward 

 Crossley, F.R.A.S., and made by Messrs. T. Cooke & Sons. 



Edward Crossley, F.R.A.S., Halifax. 



The apparatus consists of a wooden rod 6 ft. in length, with metal ter- 

 minations containing spherical cups fitting on to spherical heads upon tripod 

 stands. Three tripod stands are required. Each terminates in a flat ring 

 upon which the base of the short pillar carrying the spherical head is 

 adjustable, and to which it can be clamped. The rod is supported by two 

 tripod stands, while the third is set forward to receive the rod in its next 

 position. The inclination of the rod is read off" to ,half-a-minute in each 

 position by means of a level and arc attached to the centre of the rod. The 

 true horizontal distance is then obtained by applying a tabulated correction 

 for each inclination of the rod. 



This instrument will give an accuracy of 1 in 10,000 over any sort of 

 ground, even with a gradient of one in four. 



266. Ivory Pocket Measures. T. Hawksley. 



269. Foot-scale-plate. A rectangular brass- plate containing 

 twenty different foot-scales, made in 1769 by Adam Steitz in 

 Amsterdam. It is a copy from the original deposited in the Town 

 Hall of Amsterdam. Professor Buys-Ballot, Utrecht. 



275. Meter-measures, constructed of mica. (See Nos. 60, 

 879, 2591, &c.) Max. Raphael, Breslau. 



These measures have the advantage of being transparent, and may serve 

 for copying geometrical drawings. Owing to their remaining unaffected by 

 the ordinary changes of temperature they may also be used as standard 

 measures. 



289. Meter Scale with double divisions, for and 20 C., 

 by Breithaupt and Son, in Cassel. 



Mathematical and Physical Institute, Marburg (Prof. 

 Dr. Melde). 



295. Standard Double Meter on steel, in a case. 



F. W. Breithaupt, Cassel. 



The normal double meter is a terminal surface measure, as well as a 

 mortise-gauge, with divisions throughout in centimeters, and on both the end 

 decimeters in millimeters. This double meter is graduated on the precision 



