CLARK: HARVARD DEEP-SEA THERMOGRAPH. 525 



therefore made. The zinc cans were made by Mr. V. Seitz at the 

 Cruft Laboratory, Harvard University, and were filled and prepared 

 for use by the Secret Service Battery Company of Everett, Massa- 

 chusetts, through the kindness of Mr. F. D. Harper. Three cells are 

 required to light the lamp, but space is provided for a fourth, to be 

 used when the cells deteriorate with age. One commercial three-cell 

 lamp has been found still in good order after enduring about 2,000 

 flashes with four of the dry cells in the circuit — a battery of four cells 

 proved still useful after 800 flashes. 



Clockwork. 



The clochvork unit, Plate 4, fig. 13, was made by the E. Howard 

 Clock Company. It is arranged in three levels, and is attached to 

 the upper casting of the photographic unit. Undue strains are pre- 

 vented by making it sufficiently small so that it does not touch the 

 cover. In the upper level is the clockwork proper, that is, the time- 

 keeping mechanism, and the electrical contact device for lighting the 

 lamp. The wheels in this level are referred to as the upper train. 

 The lower level contains the lower train, which serves to roll the film- 

 spool; and the mainspring occupies the middle level. Save for a few 

 alterations the upper train is similar to that used in the stock model 

 known as the No. 16 time-clock made by the E. Howard Clock Com- 

 pany. The escapement is identical with the one used in that model. 

 It can be removed as a single unit from the clock by merely taking out 

 two screws, thus simplifying the operations of cleaning and repairing. 



The mainspring, which consists of two springs in tandem, operates 

 both the upper and lower trains. A great latitude in the use of the 

 thermograph is gained by this arrangement. The spring is designed 

 to operate the thermograph for ten hours, making a record every three 

 minutes.^ If, however, it is desired to make records over a longer 

 time, the exposures may be made at intervals as great as an hour, 

 in which case the mainspring will devote nearly all its energy to the 

 clockwork proper and will keep it going a week or more. The spring 

 communicates through the winding arbor with the lower train, the 

 first member of which is a combination of two wheels and disc on a 

 stud, Plate 4, fig. 13, a. The two wheels are connected by a ratchet, 



' If film without black paper is used, the present clockwork will run fifteen hours, with one 

 winding, giving 300 pictures. 



