Oct. 26, 1S82] 



NA JURE 



62 



The comet was well seen here on Monday, October 23, for 

 some considerable time about 5 a.m., though clouds occasionally 

 hid part of it. I noticed the following: — 1. The length that 

 was clearly visible was such, that if the head had been placed on 

 Sinus, the tail would have reached to Orion's belt. 2. The 

 lower edge of the tail was compara'ively sharp and brightly 

 defined, while there was 1 o well-defined upper edge. 3. At 

 first sight the tail ended, fairly abruptly, in a short fork. But 

 on glancing to one side, so as to allow the image to fall on a 

 more sensiiive part of the retina, one became aware that the^e 

 two forks were continued in a very faint and hazy manner as far 

 again as the length of the comet first noticed (mentioned and 

 measured in (1.)) Or, more strictly, one became aware of a 

 black rift in the sky behind the comet, in its direction, above 

 and below which the sky was faintly luminous. One may say 

 that at first sight the comet ended like a house-martin's, on more 

 careful observation like a swallow's, tail. The total leng'h of 

 the comet thus seen was enormous; and the appearance sug- 

 gested an even greater extension. W. LARDEN 



Cheltenham, October 24 



Although the fact is mentioned in Nature of the 5th 

 inst., that the comet was observed by Mr. Finlay, the Fir t 

 Assistant to the Astronomer-Koyal at the Cape of Good Hope, 

 at 5 a.m. on September b, perhaps the t .llowing graphic account 

 of its appearance, which I extract from a letter received this 

 morning from my friend Mr. G. B. Bennett, dated Waier-Hof, 

 Cape Town, September 26, may have some interest. Mr. 

 Bennett believed himself the earliest observer, but he does n >t 

 consider the comet more conspi;uous on thi-. occa-ion than it 

 was in 1843. 



" I take an especial intere t in our present visitor, as I fancy 

 that I am the very fir-t per.-on who saw it, and this was on the 

 8th inst. at 5 a.m. I was attracted into the garden by the mar- 

 vellous brilliancy of the stars. On turning my eyes eat ward I 

 detected a stranger at once ; it did not appear as a comet, but I 

 knew that there ought not to be any large stir in the sp)t 

 occupied. It was ab mt midway between Alpherat (Cor Hydra) 

 and Regulus ; ihe latter, however, was not vi.-ibie at the time I 

 called to my daughter, and asked her to put her head out of the 

 window, and she at once said, * a comet.' I then wrote a n^-te 

 to the Editor of the Cape Times announcing it; this letter did 

 not reach him, it would be long to explain why. ... It is ( f 

 such size and brilliancy as to be seen in the brightest sunshine. 

 I saw it September 18 between noon and I p.m. D.\ Gill is 

 reported to have said, ' the largest for 2CO years.' I don't 

 believe he said so ; if so, he could not have teen the one of 

 March, 1S43." 



My friend adds that he has ascertained most po itively that it 

 was not ob erved from the deck of either of the mail steamers 

 Athenian or Garth Castle, then approaching the Cape. The 

 latter carried Father Perry and the members of the Transit < f 

 Venus Expedition. " My belief is that it came within the ken 

 of human vi ion on the morning of the 8th September, and not 

 before.'' His >tation of observation, Waterhof, is about half-way 

 up Table Mountain. J. H. L.EFROV 



October 19 



Refusing to my letter of the 16th, I beg to say that the 

 R.A. of the " neighbouring object " should hive been ioh. urn., 

 and that it was probably, not Schmidt's comet, as supp sed, but 

 the 7th or 8th mag. star 199S0 Lalande, which does not appear 

 in the B.A. Catalogue, or in the V.S. Catalogue, or in the luge 

 maps of the S.D.V.K., or 1 n Mattly's Glore. Ii appeared to me 

 of much greater magnitude than the above. 



Bray, Co. Wic 1 low, Cctober 2t WENTWORTH Erck 



The magnificent comet now visible in our eastern sky shortly 

 before sunri.-e is no doul t being observed in England. In ca-e 

 it should not I may add that its approximate po-ition at 4V1. 50m. 

 a.m. (local mean time) this morning as determined by my equa- 

 torially mounted '4^ inch Cooke) tele cope was R.A. ioh. 55 1.. 

 South declination 3 1 29'. The tail by estimation is aoout 14", 

 and of unusual breadth. The borders of the tail appear much 

 brighter than the central part. H COLLtTT 



Lahore, The Punjab, India, September 25 



The Proposed Bridge over the Forth 

 It is no small evidence of the importance of this great under- 

 taking, that the proposed scheme should have drawn from Sir 



George Biddell Airy such severe criticism as that which appeared 

 in last week's Nature. Coming from such a source, this criti- 

 cism is sure, not only to receive the most careful consideration 

 of those few who are sufficiently conversant with such matters to 

 form their own opinion, but is sure to have great weight with the 

 much larger class who accept the opinion of tho e they conceive 

 best able to judge. It therefore behoves those who are respon- 

 sible for this scheme, to make the hest answer they ran. 

 Whether they will be al le to remove altogether the impression 

 adverse to the scheme, may well be doubted ; but for my own 

 part I do not anticipate that they will find much difficulty in 

 meeting the objections raised, in so far as these are definite. It 

 is not my pre ent object to defend, or even to discuss the merits 

 of the proposed bridge ; what 1 wi-h to point out is that the 

 knowledge of engineers as regards the theory of structures, is 

 not s 1 imi erfect, or their methods of designing such guesswork 

 a- might be inferred from the tone of the criticism. 



Sir George Biddell Airy expre ses alarm lest in the design due 

 consideration has nit been paid to the " theory of buckling ;" 

 but whether this is so cr not, does not appear from any circum- 

 stance to which he has re'erred. 



To make a stiut 1 r "thrust-bar" 340 feet long to ustain a 

 thrust of several hundred tons, is doubtless a stupendous un- 

 dertaking, but so is a bridge to carry a railway over 1700 feet. 

 There i-, however, no theoretical reasm again t the possibility 

 of such tinctures ; that is to say, assuming the same strength 

 and elas'ic properties of material as are experienced in existing 

 structures, it appears by the application of the principles of 

 mechanics that both such distributions and uch quantities of 

 material are possible as will assure the safety of these structures. 

 Whether or not such distribution and quantities have been 

 secured in the de igns for these stiuts, could only be judged of 

 after ca'eful consideration of the proposed lateral secti ins in 

 conjunction with the longitudinal section, and to these no refer- 

 ence whatever is made in the critici-m . 



That the experienced engineers who have n.ade themselves 

 responsible for this de.-ign cm hive overlooked such an im- 

 portant consideration as 1 uckling is very improbable. There is 

 in possible accident to structures which has reeeiv.d n^ore care- 

 ful consideration than buckling, or of which the laws have been 

 more definitely ascertained. 



The very pretty method, igiven in the appendix to the com- 

 munication under consideration, for obtaining the formula 



W = C — is a weil-known application of the theory of ela.-ti- 



o- 

 city, and is given by Bresse.' But this formula is known only 

 to apply to prismatic bar- verv thin, compared with their length, 

 r.nd is therefore c f little practical u-e. The laws of stiffness and 

 S rer.gth for s'rut- of a solid section, were first deduced by Eaton 

 Ilodgkinson from his own experiments, and have since been ex- 

 tended to struts of any section by I ewis Gordon a d Rankine. 

 For wrought iron, 'putting P for the load, S the area of 

 section, L the length, and r the least radius of gyration of the 

 section a "out any line in that section, the units being inches and 

 lbs., the formula is — 



= 36,000 



36,000 1 



From this it will be seen that L must be very large compared 

 with r before this formula a-sumes the same form as that which 

 Sir George Biddell Airy has obtained. 



Such general formulae are not, however, the only or the chief 

 g'.iiJcs i 1 modern cmstructii n ; sufficient actual <xperier.ee has 

 been cbtained as regard- 'Uch a great variety of form- for the 

 elementary parts of structures as to furnish rules for the propor- 

 tioning of every cla-s. And 1 1 h .ugh any n velty such as 

 unprecedented size furni hes matter for grave consideration, both 

 as regards proportions ai d tte pos ihilitit s of art, still the theory 

 and data for assuring reasrna'le aftty aie available, and 

 engineers u-.u I be much behind the day if they neglect these. 



Ow-ens College, Oajher 21 Osborne REYNOLDS 



I HAVE read Sir Ge age Airy's crilici m of the design for the 

 proposed Forth Bridge with interest. So far as engineers are 

 concerned the lelter calls for no re| l_v : but as others pardonal Iy 

 ignorant of ihe 1 rt sent state of engineering rcience nay feel the 



arplique," p. 210 (18 6 . 



