March 9, 1922] 



NATURE 



309 



which evokes acquired characters. Clearly internal, 

 just as much as external, stimuli evoke what are called 

 " acquired characters." 



(3) As a fact, biologists when classifying characters 

 as " innate " and " acquired " have not in practice 

 been influenced by the kind of stimuli which have 

 evoked them. As again all literature testifies, they 

 have, in accordance with popular usage, called all 

 characters which develop in response to any very 

 glaringly obvious stimulus acquired. For example, 

 they do not call the musculature of the child, the 

 youth, and the ordinary man " acquired " ; but they 

 do bestow that name on the musculature of the 

 blacksmith, though the latter develops in response to 

 precisely the same influence. Any number of similar 

 examples might be named. 



G. Archdall Reid. 



9 Victoria Rd. South, Southsea, Hants, 

 February 25, 1922. 



A Rainbow Peculiarity. 



Every one has observed a brilliantly coloured rain- 

 bow and also the secondary bow situated some 

 distance on the outside of the primary. Is it a fact 

 of general observation that the whole area of the 

 inside of the primary bow is brighter than the region 

 outside ? 



It was not until the winter of 191 3 that this bright 

 inner region was brought to my notice on a photo- 



was brighter than that on the outside. The accom- 

 panying illustration (Fig. i) gives a reproduction of 

 the photograph, 



I somewhat doubted the reality of this appearance 



Fig. I. — Rainbow photographed on December i, 1913. 



graph I secured on December i of that year. On the 

 morning of that day one or two heavy showers passed 

 from S.W. to N.E., 'traversing the ground to the north 

 of the Norman Lockyer Observatory. The primary 

 bow in question was distant about one mile to the 

 north of the observatory, as could be judged from the 

 spot where the rainbow ended on the ground. An 

 attempt was made to photograph the bow with a 

 4x5 screen focus Kodak using the ordinary Eastman 

 film, and on development it was found that the light 

 from the interior area of the bow had acted on the 

 film in a much more actinic manner than that on the 

 outside — or, in other words,' the area inside the bow 



NO. 2732, VOL. 109] 



I'iG. 2. — Rainbow photographed on December 22, 1921. 



until I had taken another photograph of a similar 

 nature, and an opportunity occurred in December of 

 last year. 



On December 22 numerous showers were passing 

 to the northward of the observatory, and I photo- 

 graphed three different rainbows during the morning. 

 They were not so brilliant as that photographed in 

 1 91 3, but yet sufficiently bright to record the same 

 phenomenon. One of these photographs is repro- 

 duced in Fig. 2, and a comparison of the intensity 

 of the distant landscape inside and outside the primary 

 bow corroborates the previous photograph. 



These photographs thus establish a fact in Nature 

 which appears to have been rarely noticed visually. 

 Kamtz in his " Lehrbuch der Meteorologie " (vol. 3, 

 p. 158), a book which was pubhshed so long ago as 

 1836, writes on the subject as follows : — " When a 

 rainbow with very pronounced colours is projected 

 against a dark cloud, the sky above the first bow 

 is darker than that underneath. If we follow the 

 path of Ught in our spherical drops and remember the 

 limiting values which have been given above, we 

 receive none of the inner surface reflected rays from 

 any drops which he higher than those in which we 

 found the maximum and which form the bright bows ; 

 lower-lying drops also send out rays from the inner 

 back surface, and, although these more or less diverge, 

 they tend to produce an undoubted brightness under 

 the bow. The drops lying above the bow also send 

 out reflected rays from their near sides, while from 

 the drops lying under the bow we receive rays from 

 the far side." 



Following this extract Kamtz states that he has to 

 thank Brandes for directing his attention to this 

 phenomenon, and gives a reference to Gehler's 

 " Worterbuch," Nach. Asir., vol. 7, p. 1324. 



William J. S. Lockyer. 



Norman Lockyer Observatory, 

 Salcombe Hill, 



Sidmouth, S. Devon. 



