142 Scientific Proceedings, Royal Dublin Society. 



the two internal total reflections, rendering the other image hardly- 

 visible; and, secondly, as there was no magnifying power, it was 

 not easy to form a correct judgment within some seconds of the 

 time at which the images overlapped. 



Some improvements have occurred to me, which I effect in the 

 following way : — 



1. By covering one-half of the. prism with a film of sulphide 

 of lead, such as we use in the new gun-sights, I am able to make 

 the two images equal in intensity. 



2. Instead of viewing the images directly, I add a lens 

 by which images of any desired size are thrown on to a wall 

 or screen. 



In the instrument exhibited, the lens is about 20 feet in focus, 

 and forms solar images of about 2 inches in diameter. These 

 images move relatively to one another at the rate of about one- 

 thirtieth of an inch per second, so that it is quite possible for even 

 an unskilled observer to register the time within a second, which 

 is sufficient for all ordinary purposes. 



A table of "Equations of Time" could be arranged con- 

 veniently to the instrument, so that the true mean time could 

 always be deduced from the solar time, as given by the instrument. 



"With these modifications, the little instrument becomes a really 

 practical tool, which will be found of considerable use in districts 

 where it is not otherwise possible to obtain correct time. 



