522 bulletin: museum of comparative zoology. 



Plate 1, fig. 2 and Plate 2, fig. 4 show the centres e, f, g, g, which 

 hold the two film-spools. The upper centres e and / are shown in 

 detail Plate 3, fig. 8, 9. One of them, e, is turned positively by the 

 clockwork, while the other,/, is somewhat restrained in its motion by a 

 spring. The lower centres, g, g, Plate 1, fig. 2, Plate 2, fig. 4, Plate 3, 

 fig. 10, 11, can be withdrawn sufficiently to permit the spools to be 

 put into place. When they are returned to position they are locked 

 by the two small cranks h, h, Plate 1, fig. 2, and Plate 3, fig. 11. A 

 spring, i, Plate 1, fig. 2, Plate 2, fig. 4, tipped with ball-bearings, keeps 

 the film and paper tightly rolled. In fig. 2 and 4 j is a red window for 

 adjusting the film for its first exposure, and b is the roller over which 

 the film passes. 



The top casting js shown together with its accessory parts in Plate 

 3, fig. 8, 9. The tube k provides space for the expansion-chamber of 

 the thermometer. Insulated studs, /, /, are connected to the batteries 

 below through spring contacts, and m is an insulated conductor to 

 carry current to the clock. Figures 10 and 11, Plate 2, show the bot- 

 tom casting with other parts. It is fastened to the back casting by 

 three screws. The cap n, which holds the battery-cells in place, 

 contains an insulated insert, as shown, to connect them in series. The 

 lamp-socket o can be removed by turning aside the connector j)- The 

 casting is fitted with a key and a latch, q, to hold the thermometer 

 in the right position. The front casting containing the optical system 

 is held in place by two bolts, r, r, fig. 11, Plate 3. They pass through 

 the bottom casting, through the holes s, s, Plate 1, fig. 3 and Plate 2, 

 fig. 5, into the top casting, and are locked in place by a quarter turn. 



Optical System. 



It would be easy to photograph the thermometer if plenty of room 

 were available. Since in a restricted space four inches of stem are to 

 be photographed on a 4-inch film, the problem can scarcely be solved 

 with lenses. The special optical scheme was devised by Professor 

 Daly. When the front casting is in place it fits over the shield t, 

 Plate 1, fig. 2, Plate 2, fig. 4, and Plate 3, fig. 11, to make a light- 

 tight joint. The lamp is then directly beneath the cylindrical hole 

 u, Plate 1, fig. 3 and Plate 2, fig. 5, which, being lined with white 

 paper, is diffusely illuminated. Parallel with this hole and connected 

 with it by a wide slot is another smaller one at v, Plate 1, fig. 3, which 

 contains the collimator, Plate 2, fig. 6. The collimator consists of 



