570 FOURTH REPORT 1834. 



state. The length of the rods, of which the expansion was 

 determined, was 23 inches, and they varied in the cross section 

 from half an inch to three quarters of an inch square : the length 

 is laid off on the heads of small silver studs, sunk into the stone. 

 The micrometer microscope of the pyrometer measures the 

 thirty-thousandth part of an inch ; and as a test to satisfy him- 

 self of the correctness of the instrument, and of the uniformity 

 of its results, the author determined the expansion of cast zinc, 

 selected, as a simple metal, having the greatest range, and his 

 determination of it agreed very nearly with that given by 

 Smeaton. He then procured a rod from a very equally-grained 

 block of sandstone, from what is called the Liver Rock of 

 Craigleith Quarry, from the same part of the bed from which 

 the large stone in the pillar of the mural circle in the Edinburgh 

 Observatory was cut ; it possessed a considerable degree of 

 flexibility when wet, but gradually stiffened as it became dry. 

 The expansion of this sandstone, as determined from a length of 

 twenty-three inches, with a range of temperature of 145° Fahr., 

 gives -0270446 of an inch for 180° Fahr., or -001 1758 in decimals 

 of its length, which is the same as the expansion of glass given 

 by Berthoud, and very nearly the same as the expansion of cast 

 iron as found by Lavoisier. Black marble, from Galway, in 

 Ireland, has the least degree of expansibility of any substance 

 which Mr. Adie has tried, with the exception of wood. He states 

 it to be -00043855 of its length for 180° F., which is rather 

 more than one third part of the expansion assigned by Lavoi- 

 sier to steel, and nearly half that of platinum and glass for 

 the same number of degrees. He also measured the expansion 

 of Carrara marble ; but as the specimen used was only one foot 

 long, he does not state the result numerically: it was less, how- 

 ever, than that assigned to it by M. Destigny. A rod of oak, 

 split from the tree to insure the straightness of the fibre, ex- 

 panded -000062007 in decimals of its length, for 1 80° Fahr., which 

 is just one fifteenth part of the expansion of platinum for the 

 same number of degrees ; an insensibility to the change of tem- 

 perature which arises very much from the wood being very 

 dry when the experiment was made. The number here given 

 is a mean of three trials, but the same rod of wood gave a very 

 different result when a very small quantity of steam was allowed 

 to blow into the case which contained it. It is Mr. Adie's in- 

 tention to repeat these and other experiments during the 

 winter, when he hopes to be able to command a greater range 

 of temperature in his instrument. He will then give a full 

 account of them, and the manner in which they have been 



