Maece 1, 1894.] 



KNOWLEDGE. 



63 



taken ; but he claims for none more than a provisional 

 character. There can. however, be little doubt that all the 

 sacred edifices in the Nile valley were built with some refer- 

 ence to the heavenly bodies. This is suggested by their very 

 structure. From the inner sanctuary of each, the line of 

 view was invariably kept clear to the horizon, whither the 

 eye was often guided through rows of massive pylons, or 

 along far- stretching avenues lined with obelisks, columns, 

 or statues. The purpose of this open light-route was 

 evidently that the rays of a rismg or setting lummary 

 might, at certain annually recurring moments, flash 

 transitorily upon the image of the enthroned divinity. 

 "Manifestations "of this kind are indeed positively stated in 

 some of the mural inscriptions to have given the signal 

 for the commencement of solemn celebrations ; hence the 

 temples were expressly planned to secure their unfailing 

 display. For the most part, it was sun-illumination which 

 was thus led captive to the shrine of the god or goddess ; 

 but; a considerable number of temples face too far south 

 or north of the equator to have ever been available for 

 solar observations. These, we are now informed, were 

 oriented, each to a particular star. Thus, there can 

 be no question but that the goddess Isis was represented 

 in the heavens by the blazing Sirius ; and it may also be 

 admitted that the temple of Isis at Dendera was erected 

 as a kind of spy-tube upon the yearly reappearances at 

 dawn of her stellar eilti-r ei/o. This took place on the 20th 

 of .Tune, the Egyptian New Year's Day, and was hailed 

 with clamorous exultation. From a comparison of the 

 actual aspect of the temple with the lie it should now take 

 in order to comply with the ancient conditions of its existence, 

 Mr.Lockyer places its foundation atabout TOOb.c. The local- 

 ization of a star naturally implies a date, since precessional 

 movements occasion a continual shifting of rising-points, as 

 viewed from any determinate spot on the earth's surface. 

 A temple, of which the axis was designed to be threaded 

 by the emerging beams of a certain star, must then have 

 been built at a strictly calculable epoch. In two, or at 

 the utmost three hundred years, it would become super- 

 annuated. The star of its cult would no longer shine 

 into it. Originally aligned with a moving object, it now 

 remains as a perennial record of the interval which has 

 elapsed since that primary, though comparatively tran- 

 sient, agreement was complete. Hence the chronological 

 value of this method, provided only that satisfactory 

 assurance can be obtained as to the individual stars to 

 which the temples were oriented. Mr. Lockyer's identifi- 

 cations are not meant to be final. The admission of 

 Canopus, it may be remarked, as an object of worship in 

 Upper Egypt, would carry the time back to 6100 b.c. A 

 great deal of research, however, including surveying 

 operations and the labours of decipherers, is requisite 

 before the brilliant suggestions contained in the volume 

 before us can be either received or rejected without 

 hesitation. 



Uttttrs. 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



IRREGULARITIES IX THE TAILS OF COMETS. 

 To the Editor o/ Knowledge. 



Deak Sir, — I have been very much interested by the 

 articles on Brooks' Comet in the last number. On the 

 one hand, it seems to me that Prof. Barnard does not 

 prove the assumption which gives the title to his article — 

 " On the Probable Encounter of Brooks' Comet with a 



Disturbing Medium" ; and, on the other hand, I do not 

 understand how the explosions you speak of, or the great 

 and sudden changes in brightness, could be caused without 

 some encounter or external influence more irregular in its 

 action than the slow increase or decrease of the sun's heat, 

 due to the comet's changing position. Prof. Barnard 

 seems to assume that the whole comet was stirred up by 

 the collision of its tail with a resisting medium. He 

 says; — "In the second photograph (see the picture for 

 October 21st) the entire comet was brighter, as if the 

 ilisturbtince had added to its lii/ht" [the italics are my own] ; 

 and he goes on to say, " as also seems to have been the 

 case with the third photograph on October 22nd, for its 

 exposure w'as much shorter, as flying clouds were obscuring 

 the sky a considerable portion of the time." No doubt the 

 rapidly-varying brightness is proved beyond dispute by the 

 photographs, but I do not see how a blow upon a comet's 

 tail could affect the brightness of its head or nucleus. If 

 the matter of the tail is, as we have hitherto supposed, 

 always streaming away from the nucleus, such a theory, 

 at all events, needs further proof than Prof. Barnard gives. 



It seems to me more probable that the irregularities in 

 the tail are as you, Mr. Editor, suggest, due to irregulari- 

 ties in the quantity of matter streaming away from the 

 nucleus, as well as due to changes in tlie direction in 

 which the streams of matter are driven forth from the 

 head of the comet. But I cannot conceive how the sun's 

 slowly increasing heat acting upon the nucleus could 

 cause such sudden outbursts in different directions. 



The phenomena presented are intensely interesting 

 because they are so mysterious. My father felt great 

 difliculty in accepting the ordinarily received theory that 

 comets have been captured from outer space and deflected 

 into closed orbits by the larger planets, because, with 

 bodies of sensible diameter like comets, the nearer and 

 further parts would be difl'erently acted upon by the 

 planets they approached, and the various parts of a large 

 group of stones would consequently be deflected into very 

 difi'erent orbits. 



The elongated nuclei of some comets, and the small 

 attendant comets which have been seen alongside some 

 large comets, seem to show that the material of the 

 nucleus has been torn into pieces by perturbations, and 

 has in some instances been stretched out into a stream of 

 nuclei or isolated clusters of stones arranged in a Ime. It 

 seems to me to be worth considering whether the notches 

 in the tail of Brooks' comet may not have been due to 

 some repelling action around an invisible attendant comet, 

 such as was observed, or, at all events, was photographed 

 by Prof. Barnard, in the midst of the tail of Swift's comet. 



It will also be seen that the ejected matter from the 

 nucleus was pretty evenly distributed on either side, as it 

 streamed away from the head of the comet, while if some- 

 thing had run against the tail of the comet, its fragments 

 would have been drifted to one side of the general axis of 

 the tail. In the second photograph, taken on October 

 22nd, the even distribution of matter driven back from 

 the nucleus is even more noticeable. 



Yours faithfully, 

 Brighton, 7th February, 1894. H.\ery Proctor. 



[Many of the older readers of Knowledge will, I feel 

 sure, jom with me in welcoming Mr. Harry Proctor as a 

 contributor to our pages. His theory, as to the possible 

 action of attendant comets, seems to me to be well worthy 

 of consideration. We know tliat some three or four comets, 

 whose paths approach the earth's orbit, are accompanied 

 by widely distributed flights of meteors distributed along and 

 around their orbits. If the matter driven from the main 

 nucleus of a comet varies in quantit}- from day to day and 



