Mr. E.J. Stone on the Heating -powers ofArcturus and a. Lyra. 379 



temperature of the thermometers has been imparted to the faces of 

 the pile when the needle is steady, provided that the current be 

 carried from the thermometers without loss in the nature of increased 

 resistance. I have therefore compared the deviations produced by 

 glass G before the faces j3 and a with the thermometers in contact 

 and without thermometers in contact with two different amounts of 

 resistance in circuit. Such observations have been considered satis- 

 factory only when the two resistances for thermometers in contact 

 and without thermometers were sensibly equal. This condition can 

 be obtained by making the thermometers touch along the lines of 

 junction of the antimony and bismuth ; but the connexion being one 

 of mere contact, there is always danger of failure. 



The following observations were made on 1869, Aug. 19 : — 



1. Without thermometers : 



Resistance = R+0003 B.A. unit. 



Mean difference, G before /3 — G before a = 73 5 div. 



2. With thermometers in contact : 



Resistance =R 1 + O003 B.A. unit. 

 Mean difference =698 div. 



3. With thermometers in contact : 



Resistance = R X + 1*437 B.A. unit. 

 Mean difference =324 div. 



4. Without thermometers : 



Resistance =R+ 1*437 B.A. unit. 

 From (1) and (4) R= 1*251 B.A. unit. 

 From (2) and (3) R x = 1*239 B.A. unit. 

 The resistances are therefore each sensibly equal to 1*245 B.A, unit. 



From (1) (2) and (3) (4) we find ^ = 1*056. 



From the mean of such determinations I find 



1=1-087. 



If, therefore, c is the distance of the pile from the cube in 

 inches, we have 



C = 155.° x 1*087. 



c 



And the heating-power of the star 



= 1^X 1 '087 X 0*725 x-. 



C 2 (f> 



I may mention that the whole area of a face of the small pile 

 may be considered effective in the focus of the equatorial. 



The following observations have been made and reduced as above. 



1869. Aug. 2. 

 Observations of Arcturus, altitude about 25°. 

 = 23 div. 

 <p=160 div. 

 c=17*6 inches. 



