Experiments on Buildmg Stones. 905 



it has a granular structure, rather coarse, and its cement is 

 argillo-ferruginous. 



To ascertain the exact lengths of these pieces at the different 

 temperatures produced by exposure to the weather, these alone 

 being important tor our immediate object, and for the purposes of 

 construction generally, the measurements were made by means 

 of a white fine rod, with copper elbows at the ends, embracing 

 the stones when applied to them, as represented in the sketch. 



r/gj 



A A is an elevation or vertical section lengthwise of the stone 

 to be measured ; B B the measuring rod, with elbows D and C, 

 of thin hammered copper, firmly secured to it. The end D was 

 always adjusted to the same part of the stone, by sliding through 

 a groove in the copper guide F cemented to the stone; the 

 elbow C was adjusted in like manner by sliding through a groove 

 in the piece E, also attached to the stone. The elbow C has 

 itself a groove, through which the wedge W may slide horizon- 

 tally under the guide E, between the elbow C and the stone. 

 This wedge being graduated as a diagonal scale, showed by the 

 distance which it entered, the difference between the length of 

 the measuring rod and that of the stone. The expansion of 

 the measuring rod being known, the length of the stone could 

 be calculated in decimals, viz. the English standard inch. 



A groove was cut in the stone, in which a thermometer was 

 placed at each measurement, and, being covered, was suffered 

 to lie some time, in order to ascertain the temperature of the 

 stone. The temperature of the measuring rod was assumed to 

 be that of the open air to which it had been exposed. 



By Lardner and Kater's Mechanics, we have, as a mean 

 between the results of Captain Kater and Dr Struve, for the 

 linear expansion of deal wood, in terms of its length, for orie 

 degree of Fahrenheit, the decimal .00000255 ; and by the Ed'm- 



VOL. XIII. NO. XXVI. — OCTOBER 1832. U 



