130 



KNOWLEDGE 



[July 1, 1891. 



You state " there is no authority for the curious equa- 

 torial mountin<i; " which I have drawn, " or for the attach- 

 ment of the suu-screen to the instrument hy a rod. In 

 fact, we know that such a mounting could not liave been 

 used." My authority is the ilkistration to be found — rod, 

 screen, and all — in the work published by Padre Soheiner 

 in 162G, called " Rosa Ursina," giving full warrant for its 

 use in Horrocks' time. The telescope is there seen fastened 

 by strings, enabling him to take it off and place it, if need 

 were, as suggested by you, but not necessarily precluding 

 its use in any other manner that might occur to the 

 astronomer who was so full of resources. The clouds, 

 which only dispersed at the late hour of his observation, 

 enabled him to take very deliberate precautions before- 

 hand for his final survey. You say the tube was evidently 

 home made ; whether that was the case or not, it was of the 

 best kind, as he states, " The telescope which I employed 

 on this occasion is much more accurate than those 

 generally used," leading to the belief that he pi-obably 

 had more than one of those instruments in his possession. 

 He probably set the telescope to the position it would 

 occupy when he came out of church, as if it had been 

 driven by clock work. 



To your final objection as to the omission of the cassock, 

 as part of his dress, I think I must plead to its being done 

 purposely, as I thought its ample folds would have inter- 

 fered seriously with the movements necessary during his 

 observation in a small room full of the accessories neces- 

 sary for the fulfilment of his purpose. 



Yours very truly, 



Eyre Crowe, A.R.A. 



[To follow Mr. Eyre Crowe, I would gladly exercise a 

 little poetic imagination, and suppose that Horrocks knew 

 the time within two minutes when he would be able to 

 finish his service and get to his rooms. The Sun appears 

 to move by reason of the earth's daily rotation through its 

 own diameter in about two minutes. Consequently, if 

 Horrocks had had modern facilities for timing his clocks 

 and accurately setting his telescope, he might have hoped 

 to find some portion of the Sun's disc thrown on the screen. 

 But in order that he should enter the room and find the 

 image of the Sun centrally on the screen, as Mr. Eyre Crowe 

 depicts it, Horrocks must either have had a telescope 

 moved by clock work, or he must have moved himself with 

 the precision of very accurate clock work, for he must have 

 entered the room within ten seconds of the time he had 

 intended and calculated for. If this is Mr. Crowe's theory, 

 why did he not give Horrocks' equatorial mounting a 

 di^'ided circle to enable him to set the instrument in right 

 ascension ? Scheiner's instrument, as shown in the " llnsa 

 I'rximi," had such a divided circle about the base of its 

 polar axis, roughly divided it is true, but it would no 

 doubt have enabled him to find a star or the Sun's place 

 within a quarter of an hour. 



I did not suggest that equatorial mountings were not 

 used in Horrocks' time. They were certainly in use before 

 telescopes were invented, as is proved by the plates in 

 Tycho Brahe's "Astro)ioiiii(f install raUr imr/uinicd," But 

 such an instrument would have been quite unsuited for use 

 in Horrocks' room. It would have needed to be out in the 

 open, or under a revolving roof, to have enabled Hori-ocks 

 to watch through the whole day with it. Horrocks says 

 that he connuenced watching from sunrise, and went on at 

 every available opportunity through the whole day. But 

 with Mr. Eyre Crowe's mounting he would only have been 

 able to see the Sun as it passed across the parts of the sky 

 visible from the centre of the room through the naiTow 

 windows. 



Mr. Crowe tells me that I have not said how large tlu; 

 disc of Venus should have been drawn. Horrocks esti- 

 mated it as about a quarter of an inch in diameter, or a 

 little more. I did not measure Mr. Crowe's picture with a 

 divided rule, but compared the body of Venus with the size 

 of the eye of Horrocks. The diameter of the iris of most 

 people is about three-eighths of an inch, or a very little 

 more. Horrocks' head is not far from the Sun's image, 

 consequently the diameter of Venus ought to have been 

 represented as about two-thirds of the diameter of the iris 

 of Horrocks' eye. But Jlr. Crowe represents it as a little 

 round black spot of perhaps a fifth of the diameter of 

 Horrocks' iris, making allowance for the fact that the whole 

 of the iris has not been shown. The disc of Venus ought 

 not to have been circular, but should have been elliptical, 

 like the foreshortened disc of the Sun. 



Mr. Crowe says that he has copied Hevelius's diagram, 

 but he has not copied the scale Hevelius gives, which was 

 so carefully drawn by Horrocks. The use of this scale 

 occupied Horrocks' attention during the whole of the 

 observation, and enabled him to measure the diameter of 

 the planet, and to determine its place upon the Sun's disc. 

 Curiously enough, Hevelius's diagram is a little inaccurate. 

 Horrocks was careful to say that he made his divided circle 

 six inches in diameter. Hevelius's diagram is about six 

 and a half inches in diameter. 



Mr. Crowe has also given an Artist's rendering of 

 Scheiner's equatorial stand, especially as to the mounting 

 of the octagonal polar axis, which could not have been 

 turned in its bearings as it is drawn by Mr. Crowe. 



I hope that my criticisms will not have the effect of 

 deterring Mr. Crowe from again attempting an astronomical 

 subject. I should be delighted to be of service to him if he 

 should again enter the field. — A. C. Eanyard.] 



BIRDS AND BERRIES. 



By the Rev. Alex. S. Wilson, M.A.. B.Sc. 

 {Continued from juii/e 53.') 



THE prevailing colours bf succulent fruits are red, 

 blue, purple, orange, and black. White berries are 

 comparatively rare. In this respect the colours of 

 fruits dift'er from those of flowers. Black, though 

 occasionally seen in violets, is rare in flowers ; 

 white, on the other hand, is common. Perhaps the 

 explanation of this dift'erence is to be foimd in the circum- 

 stance that night-blooming flowers are white to suit their 

 nocturnal visitors ; whereas, very few frugivorous birds 

 being nocturnal in their habits, we should expect a 

 corresponding absence of pale-coloured fruits. The 

 latter might, however, be readily discovered by fruit- 

 eating bats. If at any particular season we compare the 

 colours of the fruits then ripe with the tints of the flowers 

 in bloom at the same time, we cannot fail to remark the 

 greater uniformity of colour among fruits. Thus the fruits 

 of honeysuckle, wild rose, yew, and holly dift'er much less 

 in colour from each other than the contemporary flowers. 



Notwithstanding this, birds appear to recognise when 

 fruit is ripe by the change of tint it shows. We have seen 

 a rowan-tree stand for days and no birds come near, 

 although it was covered with berries ; but, directly these 

 assumed their deep orange tinge, numerous blackbirds 

 appeared and cleared the tree in a single day. 



Nature commonly avoids the superfluous. The colour 

 of the fruit in many instances does not extend over its 

 entire surface, but is confined to the exposed side ; the 

 concealed portions resembling the foliage by which they 



