January, 1913. 



KNOWLEDGE. 



the spectator as the telescope apparently brings 

 it, are here found to be practically parallel, since 

 their vanishing point, as the draughtsman expresses 

 it, is in this case extremely remote. We are thus 

 confronted with a condition of things which in the 

 ordinary way of life would be beyond the critical 

 limit of vision. But now comes an interesting 

 psychological moment ; for the mind insists upon 

 continuing its usual operation even under the 

 present unusual circumstances. Knowing the two 

 ends of a house to be of equal size, we make a habit 

 of mentally enlarging the reduced image of the 

 distant end to fit the near end ; and here, where 

 there is practically no dissimilarity between the 

 retinal pictures of the two ends, we persist in 

 mentally enlarging the distant end, with the curious 

 result that the lines of the house appear actually to 

 diverge as they recede from us. But that this 

 astonishing effect is nothing but a psychological 

 illusion, anyone can easily prove for himself by 

 simply holding the picture in such a position that 

 the eye can glance obliquely down the seemingly 

 divergent lines, when he will at once become 

 aware that they are practically parallel ; the 

 actually existing, but extremely slight, convergence 



towards the distant end being quite inappreciable. 



To a lesser degree the same effect may be traced 

 in the appropriate portions of the other telescopic 

 pictures, notably in the right sides of the Villa degli 

 Angeli (see Figure 10) and the Villa Torrosa (see 

 Figure 11), while it is instructive to note how per- 

 sistently the illusion of divergent receding lines re- 

 asserts itself in each of the photographs, although 

 we may convince ourselves with compasses and 

 ruler that geometrical orthodoxy in reality reigns 

 supreme. 



This is a striking confirmation of the truth that 

 the same personality enters into the examination of 

 a photograph which is known to exist in the actual 

 observation of nature, and the interesting fact is once 

 more brought home to us in the study of such 

 unusual phenomena as the present, that things are 

 apt to change their seemings to suit our preconceived 

 opinions concerning them ; for our judgment is to a 

 great extent a process of semi-conscious inference 

 based upon a variety of circumstances drawn from 

 our past experience and sense of association. We 

 may, indeed, reverse the old saying in such a 

 case as this and claim that, here at least, Believing 

 is Seeing. 



A- HEN OSTRICH WITH PLUMAGE OF A COCK. 



By F. W. FITZSIMONS, F.Z.S., F.R.M.S. 

 (Director of the Port Elizabeth Museum.) 



In April, three years ago, at a caponizing demonstra- 

 tion at Graaff Reinet, Cape Province, at which there 

 were over forty farmers and townsmen present, 

 Veterinary Surgeon Elley removed the ovaries from 

 three hen ostriches. 

 The hens were each 

 four years of age at 

 the time. Shortly 

 after the operation 

 the three hens began 

 to assume the black 

 hod}- plumage of the 

 adult cock bird, and 

 from the character- 

 istic drab colour of 

 the feathers of a 

 female, these feath- 

 ers turned jet black 

 and became glossy 

 as in the male. 

 Another remarkable 

 thing happened. 

 The wing and tail 

 feathers also 

 changed, and be- 

 came so like those 

 of the cock bird that 

 feather experts, to whom they were shewn, declared 

 them to be the typical feathers of a cock ostrich. 

 These hen ostriches belong to Mr. W. Rubige, a 



Figure 13. A Hen Ostrich with the plumage of a Cock 



well-known Graaff Reinet farmer, and he kindly 

 consented to have one of them chloroformed and 

 presented tothe Port Elizabeth museum for exhibition. 

 The bird was sent to us in the flesh, and I had the satis- 

 faction of making a 

 personal examina- 

 tion to make quite 

 sure it was a female. 

 There are many, 

 no doubt, who 

 will be sceptical, 

 but I can assure 

 them there is abso- 

 lutely no doubt 

 about the bird being 

 a female. In the 

 accompanying pho- 

 tograph, the hen 

 bird is shewn after 

 it was mounted by 

 my taxidermist. 



It will thus be 

 seen that the re- 

 moval of the ovaries 

 in these three in- 

 stances caused re- 

 markable constitu- 

 tional changes. Hitherto we have supposed that 

 the ovaries, as their name implies, were concerned 

 only in the production of ova or eggs. 



