L86 Loomis — Effects of Changes of Temperatuv 



e on 



the bar to the other, the steps will be of equal length. By- 

 loosening a screw the coils may be moved from the middle of 

 the magnets to either end at one step. The cross-sections of 

 two cylindrical double boxes, made of sheet zinc, are indicated 

 at S and T. At K,K are openings in which corks holding 

 thermometers were inserted. At L,L are openings into the 

 spaces between the two parts of the double boxes. Through 

 these a current of steam or cold water was passed to keep the 

 space containing the magnets at the requisite temperature. 

 The temperatures employed were 14° C. and 99°*5 C. City 

 water direct from the faucet was used to produce the lower 

 temperature, and a fairly constant temperature was easily 

 maintained. NM,NM, are other openings by which the mag- 

 nets were introduced and through which the bars DD and PP 

 passed. They were about 2*5 cm in diameter and 20 cm long, and 

 were stuffed with cotton, the better to maintain the tempera- 

 ture of the interior. The exploring coils were connected up 

 with an ordinary astatic galvanometer of rather low resistance 

 in such a way that the currents induced by moving them along 

 the magnets opposed each other. An earth inductor and a 

 resistance box were included in the circuit, and in each experi- 

 ment the galvanometer readings were standardized by the earth- 

 inductor. Beginning at the middle of the magnets, the coils 

 were moved step by step to one end, the throw of the needle 

 being observed for each step. The coils were moved so far in 

 the last step that practically no lines of induction passed 

 through them, as was determined by experiment. Similar 

 observations were made for the other half of the magnets. In 

 this way was measured the excess of the number of lines of 

 induction passing from a certain section of one magnet into 

 the air over that passing out of the corresponding section of 

 the other magnet, thus giving the difference of distribution in 

 the two magnets. These measurements are taken first when A 

 and B are both at 14° C, and again when A is at 14° C. but 

 B at 99°'5 C. The difference between the two sets after they 

 have been reduced to the same scale by the earth inductor 

 readings is evidently the change in distribution in B due to 

 the change in temperature. By this method the quantity 

 observed is of about the same magnitude as the quantity we 

 desire to obtain ; the greatest throw of the needle was but little 

 over twice the largest difference obtained on subtracting the 

 two sets of observations. 



To get the distribution of magnetism of the bars, the differ- 

 ence in distribution was first measured as above indicated, then 

 the connection of the coils was changed so that the currents 

 induced in the two coils were in the same direction, and the 

 sum of the distributions was obtained in the same way. In 



