406 Proceedings of the Royal Society 
another horizontal piece near the bottom by the summer concavity 
and the vernal convexity. Hence in the autumn the waters of a 
deep lake are expcsed to all the different conditions of the four 
seasons of the year. In the deeper layers heat is propagated down- 
i’iG. 1. — Typical Curves ot Distribution of Temperature in a Fig. 2. — Curves of Temperature, 
Scottish Lake 100 fathoms deep. A, in winter; B, in 18th August 1885. 
spring ; C, in summer ; ai d D, in autumn. 
