1887.] Heat Dilatation of Metals from Low Temperatures. 299 



The anterior body-cavity is now small and lies near the oral end 

 in the body-wall. Into it opens the water-tube or stone-canal, which 

 runs from the water- vascular ring in the oral longitudinal mesentery, 

 and is distinguishable from the anterior body-cavity by its higher 

 epithelium. It is not, therefore, in direct continuity with the water- 

 pore. The anus opens externally in the same interradius as the 

 water-pore. 



The Skeleton remains to be described. Shortly after the orals and 

 basals have appeared, three small plates are developed at the posterior 

 end of the stem, which resemble the basals in form but are not 

 derived from them. They are so arranged that the most dorsal, 

 which is smaller than the other two, lies on the right side opposite 

 the interradius of the water-pore. These three plates are the un- 

 doubted homologues of the under-basals of the dicyclic Crinoids 

 (Poteriocrinus, Encrinus, Sfc). Shortly after the fixation of the larva 

 they fuse with one another and with the top stem- joint, so as to form 

 a large plate which has hitherto been mistaken for a simple centro- 

 dorsal. The five radial angles of this plate belong to the under- 

 basals, and it is only at a much later period that these angles are 

 hidden by the growth of the true centrodorsal (= top stem-joint)? 

 the angles of which become interradial when its cirri appear. 



IV. "Heat Dilatation of Metals from low Temperatures." By 

 Thomas Andrews, F.R.S.E. Communicated by Professor 

 G. G. Stokes, P.R.S. Received November 30, 1887. 



It is understood that the coefficients of heat dilatation increase 

 with rise of temperature ; but Professor P. G. Tait, in his recent 

 work on ' Heat,' p. 87, remarks that " we are not aware of any 

 experiments made with a view of deciding whether, as is probable, 

 these coefficients become gradually less as the temperature is lowered 

 below zero" (0° C). 



The following experiments were made to investigate the subject in 

 relation to metals of the iron and steel series. The varieties 

 of modern steels manufactured by recent processes manifest pro- 

 perties sufficiently diverse as almost to constitute them distinct groups 

 of metals, although for practical purposes they are conveniently 

 grouped under the generic name of steel. Some of these modern 

 metals have recently been so largely used for constructive purposes 

 that the author considered it desirable to obtain an approximate 

 quantitative estimation of their dilatation by heat through varied 

 ranges of temperature. The rolled metals under observation in the 

 experiments consisted of round polished bars, 3 inches diameter, and 

 13 inches long, planed perfectly square at each end ; they were care- 



VOL. XL3II. z 



