366 PROCEEDINGS OP THE AMERICAN ACADEMY. 



At two opposite points on the inside wall of the box are projections 

 into which vertical holes are bored for the insertion of thermometers. 

 These holes are 8 cm. deep and .75 cm. in diameter, and are filled with 

 mercury which thus surrounds the thermometers. In the covers are 

 holes exactly coinciding with the thermometer holes. 



As already stated, the heating is done electrically. This is accom- 

 plished by means of coils of German silver wire, .035 cm. in diameter, 

 which surround the iron box on five sides. These coils are suspended 

 on supports made of glass tubing fastened to the sides of the enclosing 

 box. 



This enclosing box B (Figure 2) is made of sheet copper, the dimen- 

 sions of which are 23 X 23 X 32 cm. There are holes for windows, 

 thermometers, shafts, and tubes corresponding to the holes in the 

 iron box. 



The copper box is in turn enclosed in a wooden box or case, the space 

 between the copper and wood being packed with magnesia. 



The external dimensions of the wooden case are 35 X 35 X 43 cm. 

 Where the fan shafts pass through the magnesia, metal tubes were in- 

 serted and the magnesia was moistened with water so that when hard the 

 tubes were held in position. These tubes serve to prevent the magnesia 

 from falling upon the shafts. 



It will readily be seen that, on account of the numerous holes in the 

 iron box as well as in the enclosing box, a liquid bath for heating is out 

 of the question. There is no doubt that a liquid may be stirred more 

 easily than air; but after all efficient stirring means the rapid and con- 

 stant moving of the heated substance from the source to the body under 

 experiment. In the heater used, this is accomplished by a system of 

 sixteen fans of sheet iron, carried on six shafts which are run at high 

 speed by an electric motor. These fans are about 7.5 cm. in diameter 

 and create a strong circulation in the heated space around the iron box. 

 There are two fans inside the iron box to ensure uniformity of tempera- 

 ture. This is necessary on account of the breaks in the continuity of 

 the iron box. The shafts for the fans are made of steel rod about 

 .3 cm. in diameter and run in bearings screwed to the outside of the 

 wooden case. The shafts for the inner fans have their inner bearings in 

 the iron box itself, and these bearings are oiled by means of oil tubes 

 which project through the wooden case. 



In the bottom of the case was screwed a heavy iron plate G, in which 

 were fastened the steel pillars E, which support the iron and copper 

 boxes. These pillars are 16 cm. long and are .6 cm. in diameter for a 



