ox DRAWING, WRITING, AND MEASURING. Ill 



been found more difficult than Mr. Laplace's statement would lead us to sup- 

 pose it, and we cannot depend on any measurement of it as totally exempt 

 from an error of the ten thousandth part of the whole. 



• The metre, as definitively established by the government of France, is equal 

 to 39',i^^ English inches, measured, as it has been usual in this country, 

 on a standard scale of brass, at the temperature of 62° of Fahrenheit; while 

 the French, on the contrary, reduce the length of their measures to that 

 which they would acquire at the'freezing point. Hence ten thousand inches 

 are nearly 254 metres, a thousand feet 305 metres. The length of the pen- 

 dulum vibrating seconds in London, was found by George Graham, from a 

 mean of several experiments, all agreeing very nearly together, to be 39-r^ 

 inches. This is also nearly a mean between the length which may be de- 

 duced, with proper corrections, from Borda's experiments at Paris, and Mr. 

 Whitehurst's experiments made in London, with the apparatus invented by 

 Mr. Hatton, where the length ascertained is the diiference between the lengths 

 of two pendulums vibrating in different times. Mr. Whitehurst's measures, 

 however, require some corrections, which Mr. Nicholson has pointed out. 

 The fall of a heavy body in the first second appears, from this determination 

 of the length of the pendulum, to be sixteen feet one inch and a tenth. 



Of the old French measure, 15 inches made nearly 16 English, and 76, 

 very exactly, 81 ; the toise was 76 -,^0^ inches. In Germany the Rhinland 

 foot is generally used ; 100 of these feet make 103 English. 



A wine gallon contains 231 cubic inches; an ale gallon is the content of 

 10 yards of a cylindrical inch pipe. 



A variety of instruments are used for the immediate comparison of the 

 standard measure, or its parts, with other lengths or distances. Such arc 

 scales, simple and diagonal, verniers, micrometer screws, beam compasses, 

 rods, lines, chains, and measuring wheels. The greatest accuracy has ge- 

 nerally been supposed to be obtained, in large distances, by means of rods, 

 made of glass or of platina, in order to be less susceptible of such changes as 

 are produced by variations of temperature; General Roy, however, found 

 that a steel chain was as little liable to error, as any mode that he could em- , 



