ON A QUARTZ THREAD GRAVITY BALAM I. 



23'J 



Specimen Obsemation. 

 NATURAL Maximum. December 20th, 1898. 



The time between the first indication of a fall of temperature and a fall of the image 

 of the lever end may be anything between and 12 minutes, depending on the rate 

 at which the temperature is changing. The temperature when the image of the 

 lever end first gave signs of coming down, has been 0'02 below its maximum value, 

 though it is generally much less. We assume that the maximum value of the 

 temperature corresponds to the maximum reading of the vernier arm an assumption 

 which can only be rigidly justified by the accordance of the results which the procedure 

 gives. To distinguish the observation of a maximum temperature and a maximum 

 reading when the temperature alters naturally, from readings taken in other ways, we 

 call the former a natural maximum observation. As the hour at which the tempera- 

 ture rate reverses varies greatly from day to day, the preliminary watching of the 

 temperature is rather tedious. 



A minimum reading may be obtained in a similar way by waiting until lx>th the 

 temperature of the air and of the box are falling, the temperature of the air being 

 lower than that of the box. This occurs, of course, every evening after sunset. It is 

 easy now to increase the temperature of the air of the room, by using lamps or small 

 stoves ; the lights necessary for observation are generally sufficient. The temperature 

 of the box, and the position of the vernier arm, then go through minimum values 

 which are observed as before. A reading taken under these circumstances we call a 

 natural minimum. The actual observing for a natural minimum does not take 

 half-an-hour. 



