524 bulletin: museum of comparative zoology. 



^Yhen not in use the stem and bulb are protected by brass caps, 

 Plate 4, fig. 12. Several interchangeable thermometers, each 

 properly mounted, should accompany the instrument. 



Films and Battery. 



The temperature records on the film are about .1 inch apart. A 

 10-hour record of temperatures taken at 3-minute intervals requires 

 23 inches of film. This quantity of film, together with the necessary 

 black paper, can be made into a roll somewhat smaller in diameter 

 than those on the market. To save room the special spool, Plate 4, 

 fig. 12, is used. It carries a film four inches wide, and has an outside 

 diameter of | inch. These spools fit better and run more smoothly 

 than commercial ones, a necessary consideration since they are turned 

 by clockwork of limited power. 



When film which is attached to paper in the usual way is rolled from 

 a full spool to an empty one, the portions of paper and film between the 

 spools quickly become unequal in length. Instead of lying flat against 

 the paper the film buckles. Reference to Plate 1, fig. 3 shows that 

 the position of the film at the point of exposure is determined by the 

 steel roller b. To prevent buckling, so that the film may lie close to 

 the roller, a special method of attachment is used. The film is at- 

 tached at both ends, an excess of paper being left between the places 

 of attachment. The extra paper forms a plait or fold when the film 

 is put on a spool. When the film is unrolled in the thermograph, this 

 plait unrolls so that the film is held taut. When all the film has 

 reached the second spool the extra paper forms a plait at the other end 

 of the film and rolls up neatly. These special rolls are quickly pre- 

 pared by a device not here described. 



If, on the other hand, black paper is dispensed with and the naked 

 film is inserted in the dark room, about 55 inches of film can be accom- 

 modated and wound off by the clockwork. In practice it may be 

 found most convenient to use naked film, thereby also lessening 

 friction and the danger of jamming during a long run. Ordinary 

 10-exposure, four by five Kodak film-rolls may be used. 



Small dry cells furnish the current for the electric lamp. An ex- 

 posure of 2 second produces a photograph, so a battery giving two or 

 three minutes of intermittent service will suffice for a day's work. 

 At the time when the thermograph was designed very small cells were 

 not on the market. Special cells like those shown, Plate 4, fig. 12 were 



