at the total solar Eclipse in 1882 343 



tube CBAE, of silver and -inch in diameter. At E, and 

 from E to F its diameter is i inch, and this carries the steam 

 dome, which is a glass tube closed at one end and inserted 

 into the part EF, where it is fixed with a screw collar and 

 washer. The steam tube passes axially through the whole 

 instrument, terminating just inside of the glass dome. The 

 steam condensed in it runs out at the lower extremity L and 

 is received in a graduated tube in which it is measured or 

 weighed. The glass reservoir Z, which is shown hanging 

 from the outside rim of the reflector, is connected by an 

 india-rubber tube with the bottom of the condenser and the 

 instrument becomes a U-tube, of which the reservoir and 

 india-rubber connection are one limb and the condenser and 

 boiler the other. The instrument is thus easily filled with 

 water and the height at which it stands in the space EF is 

 regulated by means of Z. 



When the instrument is going to be set in action it is 

 pointed axially to the sun. When in this position, the tube 

 EF throws a strong circular shadow on the top of the main 

 condenser CB, and concentric with it. With the rotation of 

 the earth the axis moves away from the direction of the sun 

 and the shadow becomes eccentric. The appearance of eccen- 

 tricity strikes the eye at once, and it is rectified by a slight 

 motion of the instrument round its polar axis. The instrument 

 requires adjustment every two or three minutes. 



When pointing truly to the sun all the rays which strike 

 the reflector are reflected on the length AB of the axis. But 

 the boiler tube having a radius of -inch intervenes and 

 receives these rays on its blackened surface. The rays 

 reflected from the inner extremity of the inner mirror are 

 reflected on a part of the boiler tube a little below the line 

 BB. 2 , and those reflected from the outer extremity of the outer 

 mirror are reflected on a part of the boiler a little above the 

 line AB 3 . This is due in both cases to parallax. 



When the sun's rays strike the surface of the boiler, those 

 that are not thrown back again are absorbed by its blackened 

 surface and passed by conduction through the metal to the 

 water which occupies the space round the steam tube. When 



