48 Dr W. Scoresby on Prismatic Colours in Dew Drops. 



On Prismatic Colours in Dew Drops. By the Rev. W. 

 Scoresby, D.D., F.R.SS. Lond.and Edin., and Member of 

 the Institute of France, &c. Communicated by the Author. 



In a communication which appeared in the New Edinburgh 

 Philosophical Journal for 1841, vol. xxxi., p. 50, I described 

 a new method of observing the prismatic colours in the drops 

 of dew deposited upon grass or other herbage, and the 

 exquisitely rich and varied colours observed when the drops, 

 receiving the rays of clear sunshine, are examined, in proper 

 aspect, by means of a pocket telescope. 



Since the period of my former communication, I have been 

 in the habit, incidentally, from time to time, of repeating the 

 observations in this interesting department of optics, when- 

 ever the circumstances were of a nature to afford any strik- 

 ing varieties in the phenomena. Two very marked and in- 

 teresting varieties have since been observed, the description 

 of which, I trust, will not be deemed unfitting as a supple- 

 ment to my former paper. 



1. The first of these varieties, now to be noticed, consisted 

 in the beauty and diversity of the colours exhibited by minute, 

 but regularly and thickly distributed, globules of dew on the 

 surface of the leaves of plants horizontally spread. These were 

 first observed in a morning in September, some years ago, 

 and about two hours after sunrise, when a fog lay thick in a 

 valley below my residence ; but clear bright sunshine pre- 

 vailed on the elevated ground. After a warm day, the night 

 had been unusually cold, with a clear sky, and in the morn- 

 ing a very thick dew was found to be spread over the her- 

 bage and on the ground. I sought for some time for some 

 additional phenomenon in this species of optical beauty, and 

 examined, without success, a good many plants with leaves 

 spread out flat on the ground, and thickly overspread with 

 minute drops of dew. But, after many unsuccessful efforts, 

 perceiving that, when looking down upon the horizontally 

 spread leaves of the columbine, there was a strong glossy 

 appearance and reflection of light, I applied my telescope 

 to the object, but it was too near even for its short focal 



