70 Experlmcnta mudi' to dftfnnlne 



the glass by ^Hgt^ of an inch, so that its absolute expansion 

 must be '0004^6; while the white marble had lengthened more 

 than the glass had by soss^'^j so that its absolute expansion 

 came out 001072, or two and a quarter times that of the Lu- 

 cullite marble. 



Here it may be noticed, that both of the expansions as given 

 by the glass are greater than those given by the wooden com- 

 pass, and that the discrepancy is greatest on the Carrara mar- 

 ble; and we are, therefore, warranted in inferring, tliat during 

 the time, short as it was, in which the wood was exposed to a 

 moist and heated atmosphere, it had suffered a sensible expan- 

 sion or twist. 



The glass compass, having been furnished with two handles, 

 was never removed from the fluid which surrounded the marble ; 

 its extreme lightness, when among water, and the shortness of 

 the attached points, removed all risk of the error arising from 

 bending; so that the results obtained by its means seem worthy 

 of dependence, it being kept in mind that they are yet liable to 

 a very small inaccuracy that may exist in the determination of 

 the expanslveness of the glass itself. 



The experiments just detailed formed the last of three series, 

 the results of all of which gave very nearly the same expansions. 

 We have given the last, not as made with greater care, but as 

 having had the advantage of additional experience in conduct- 

 ing them. In one of the former experiments, we heated the 

 water by means of two large choffers ; yet, with all the assist- 

 ance which two pairs of bellows could give, we were unable to 

 sustain the temperature higher than at 197°. In the last expe- 

 riment we used seven spirit-lamps, and were not a little sur- 

 prised when; to restrain the too violent ebullition, we had to re- 

 move, successively, four of them, and found that three spirit- 

 lamps kept up a brisk boiling in a trough whose dimensions 

 were 37, 4, and 3| inches. 



The difference between the expansions of black and of white 

 marble is remarkable, considering the small difference which 

 exists between their chemical compositions ; but, on inquiry, we 

 found that marble-cutters, aware not only of the expansion of 

 marble in general, but of the superior expanslveness of the 



