Constants of Igneous Hock, 185 



metallic screw Kkdd passes from a lower to an indeterminable 

 higher temperature. I hope, however, in the future to obtain 

 an estimate for this discrepancy, by measuring a given amount 

 of thrust through the sight-tube with the cathetometer, and 

 comparing this value with the corresponding value to be read 

 off on the vertical micrometer. Hollow screws and water 

 circulation would be exceedingly difficult to attach here. 



Results. 



15. Arrangement of the Tables. — In the following tables I 

 and t' denote the length and radius of the (cold) fusion-tube, 

 and X ' the bulk value (water measurement) of the mean 

 depth of the meniscus, these measurements being made on the 

 day after the fusion experiments. The temperatures at the 

 bottom, the middle, and the top of the fusion-tube are given 

 under 1} 2 , 3 , respectively. For each value of mean tempera- 

 ture 6, two data for the apparent expansion of the rock, for 

 the volume-expansion of the fusion-tube, and for the actual 

 volume-expansion, (v t — v )/v — Bvlv QJ of the rock are given, 

 and they were obtained before and after the intermediate 

 temperature measurement, respectively. Reference is thus 

 made to unit of volume of solid rock at zero Centigrade, 

 throughout. The data enclosed in parentheses show that for 

 them, the value applied for the expansion of the fusion-tube is 

 obtained as a mean result of all the measurements made, 

 otherwise the value directly observed was directly applied. 

 The chief constants are summarized at the end of each 

 table. 



16. Contraction of Diabase. Series I. and II. — The results 

 of these series, being of inferior accuracy and serving chiefly 

 to substantiate the remarks of § 14, may be omitted here. 

 They showed a liquid volume-expansion of 50/10 6 per degree, 

 a solid expansion of 20/10 6 per degree, and a solidification 

 contraction of about 3 per cent, only, owing to the occurrence 

 of dilatational strain. 



17. Contraction of Diabase. Series III., Tables. — This work 

 was done on October 20, 1891, and the data are given in 

 Table II. Precautions for slow cooling were fully taken, and 

 the solidification point is therefore sharply apparent. The 

 results will be discussed in connexion with the next series. 



Phil. Mag. S. 5. Vol. 35. No. 214. March 1893. 



