OBSERVATIONS OF THE ZODIACAL LIGHT. 437 



XXXIII. — Observations of the Zodiacal Light. 

 By Thomas Heelis_, Esq., F.R.A.S. 



Read before the Physical and Mathematical Section, March 3rd, 1864. 



In the course of two or three voyages which, in the years 

 1 86 1 and 1862, I was called npon to make, I had oppor- 

 tunities of studying this remarkable phenomenon in lati- 

 tudes in which it is seen to great advantage, and under 

 circumstances which allowed of a continuous series of 

 observations, such as is seldom, if ever, possible in Europe. 

 I am well aware of the difficulty which such an object pre- 

 sents, and of the different results which will be attained 

 by any two observers in the study of it, and hence I feel 

 considerable diffidence in bringing my observations before 

 the Society ; but as I have in all cases taken care to note 

 the lesser rather than the greater limit of the phenomenon, 

 and have compared the observations with a map of the 

 stars which have been used for determining the boundaries 

 of the light, I am not without hopes that the errors of my 

 eye in failing to detect the extreme boundaries may be 

 constant and capable of elimination, and that the excellence 

 of my opportunities will enable me in some small measure 

 to add to what is already known on the subject. 



I originally left England in the month of August 186 1, 

 on a voyage to Constantinople and Smyrna, and reached 

 England again at the end of September. This voyage 

 only yielded one observation of the light, which was made 

 in Smyrna Bay, and was communicated to the Society 

 soon after my return. I subsequently left England for 

 Calcutta in the middle of November in the same year, 

 making the passage round the Cape of Good Hope. On 

 this passage I obtained no observations of the light ; but 

 afterwards, during a voyage from Calcutta to Hong Kong 



