438 MR. THOMAS HEELIs's OBSERVATIONS 



and back, I obtained a fairly continuous series of observa- 

 tions, to which, on my passage home, also round the Cape 

 of Good Hope, I made various additions. During my 

 voyage home, the late Captain Jacob was on his voyage out 

 to Bombay, en route for Poonah ; and I have examined his 

 observations, as communicated by Prof. C. P. Smyth to the 

 ' Monthly Notices of the Royal Astronomical Society ^ in 

 December 1861, and compared such as were made on the 

 same days with my own. 



The following Table gives the observed positions of the 

 apex of the light, and its length when one (or the inner) 

 cone only was observed. I have added also to this Table 

 the times and places of observation, and the observations 

 of the inner cone of light in cases in which the envelope 

 has been observed — of which phenomenon more hereafter. 

 In all cases I have used the approximate mean time at ship, 

 taking her position as that determined at the nearest noon. 

 Thus, in cases in which observations were made in early 

 morning and on the following evening, the place of the 

 ship will appear to be the same in both cases ; but as this 

 seldom happened except when the weather was very settled, 

 the preceding and subsequent places of the ship will allow 

 of her exact position at the time of observation being esti- 

 mated with considerable precision. Any attempt to give 

 the places with more precision would have necessitated 

 extracts from the ship's log and the working of the dead 

 reckoning, in every case, to the hour of observation ; but 

 this labour seemed needless. 



