Clark. — Harvard Deep-Sea Thermograph. 



PLATE 2. 



Fig. 4. Another view of main casting shown in Fig. 2. 



Fig. 5. View of interior of the front casting. 



Fig. 6. System of horizontal plates in the coUimator. 



Fig. 7. Print from original negative; silhouette of mercury column shown 



in white. 



Figures 4, 5, and 6 have uniform scale: 47 per cent of natural 



size; figure 7, natural size. 



