September 13, 1906] 



NA TURE 



489 



" G. H. B. ") are essentially dedicated to the effective 

 research of particular solutions of dynamical equatiois. 

 Not a word is said of transformations, mixed forms, &c., 

 and ignoration of coordinates is mentioned :>nly in the 

 preface, because this was Routh's point of view in defining 

 and studying the stationary motions. 



T. Levi-Civita. 

 University of Padua, August 29. 



I DO not recollect by whom the phrases " ignoration of 

 coordinates " and " ignored coordinates " were originally 

 introduced, but on consideration I am of opinion that they 

 are singularly inappropriate ones, and I much prefer the 

 phrase " kinosthenic coordinates." 



The advantages of the mixed transformation are that, 

 whenever a generalised momentum is known to be constant, 

 the motion can be determined without knowing anything; 

 about the coordinate or the velocity corresponding to this 

 momentum. The first trace I can find of this idea is 

 contained in a paper published by Lord Kelvin about 1872 

 (see " Hydrodynamics," vol. i., p. 177). 



The discovery of the mixed transformation was the result 

 of certain hydrodynamical investigations relating to cyclic 

 irrotational motion, but the circumstance that I originally 

 published it in a hydrodynamical form may have obscured 

 the character of the result as a general theorem of 

 dynamics. A. B. Basset. 



September 4. 



The alleged Triassic Fcraminifera of Chellaston, near 



Derby, 



In Nature for July 26, in a notice of Mr. Fox- 

 Strangway's memoir on the Loughborough district, refer- 

 ence is made to certain Foraminifera of Liassic type, at 

 one time believed to come from the local Trias. Prof. 

 Rupert Jones, F.R.S., has kindly directed my attention to 

 his explanation of the matter in the " Foraminifera of the 

 Crag," part ii., p. 161, published by the Palsontographir.Tl 

 Society in 1895. He there gives a history of the observ- 

 ations, including personal inquiries, and believes that the 

 Foraminifera in question came from Liassic clay in 

 Leicestershire, which was " inadvertently thrown in with 

 the ' red clay ' onits journey to Cubitt's works in London." 

 Mr. Fox-Strangways gives a reference to this passage, 

 but does not quote it, and suggests on his own part that 

 the Foraminifera may have come from Liassic material in 

 the drift. Grenville A. J. Cole. 



White- and Brown-shelled Eggs. 



Birds which lay their eggs in comparatively unprotected 

 places and in a hollow in the ground, as is the case with 

 the pheasant, partridge, jungle fowl, &c., always lay 

 coloured eggs closely resembling in tint the colouring of 

 their surroundings. White-shelled eggs are laid only bv 

 birds which make a good nest — those which make it in a 

 secluded spot, or which take the precaution of covering their 

 eggs with leaves, &'c.. when they are off the nest. It is a 

 strange fact, therefore, that the non-sitting breeds of our 

 domestic fowls lay white-shelled eggs, whereas in the eggs 

 of the sitting or Asiatic breeds the protective colouring is 

 retained in the shell of the egg. This loss of colour 

 cannot be merely the result of centuries of domestication. 

 or all breeds of domestic fowls would lay white-shelled 

 eggs. The systematic repression of the maternal instincts 

 of the hen carried on by man for a number of years has 

 certainly produced the white-shelled egg. It would almost 

 appear to be the case that the hen, knowing she will have 

 nothing to do with the hatching and rearing of the chicken 

 in the egg, loses all interest in the egg, and leaves it, as 

 it were, to its fate. For this reason she neglects in some 

 mysterious way to impart to the shell the protective colour- 

 ing which is so necessary, in a state of nature, for the 

 preservation of her race. If this be reallv the case there 

 is an insurmountable obstacle in the way of obtaining 

 brown eggs from the non-sitting breeds of domestic hens, 

 and poultry keepers are only wasting time in trying to 

 accomplish the impossible. L. M. F. 



NO. 1924 VOL. 74] 



FLASHLIGHT PHOTOGRAPHS OF WILD 

 ANIMALS. 



FROM the popularity of his well-known work 

 " Mit Blitzlicht unci Btichse " (or its English 

 translation, " With Flashlight and Rillc "), there is, 

 we believe, a very general impression that Mr. C. G. 

 Schillings was the pioneer in the practice of photo- 

 graphing big game animals by night in their native 

 haunts by combining the use of the flashlight with 

 the camera. It appears, however, from a most 

 interesting and profusely illustrated article in the July 

 number of the National Geographic Magazine that 

 the true claimant to this position is an American 



light en bushes 



sportsman, the Hon. George Shiras. With regard to 

 his position in the matter of flashlight-photography, 

 Mr. Shiras writes as follows : — 



" While a number of the present illustrations were 

 taken in the daytime, this method of photography is 

 now so well known that I will not attempt to describe 

 such pictures in detail ; but in view of the fact that I 

 was the first to attempt flashlight pictures of wild 

 game, and for the first fifteen years was the sole 

 occupant of this attractive field of photography, it may 

 be of interest to the readers of this article to learii 

 something about this rather odd wav of picturing- 

 wild animals." 



