Oct. 1 6, 1884] 



NATURE 



583 



At least so I understand his letter in Nature, vol. xxx. p. 536. 

 If that statement or conclusion is perfectly correct, I must of 

 course allude to it in the next edition of my Pyramid book, 

 and adopt its corrections, whatever they may lead to ; so that it is 

 well at once to ask any further questions which seem demanded 

 for full trust and credibility. 



That the observations made at Greenwich during the last 

 forty-seven years, when computed as the said Astronomer-Royal 

 has computed them, do not show any change of latitude during 

 that space of time, no one is more ready to allow most honour- 

 ably than myself. But before we can admit that that result, 

 pure and simple, absolutely establishes the non-shifting of the 

 earth's axis of rotation, two more things at least must come 

 about, viz. : — 



First, the Astronomer-Royal must attack and demolish the 

 observations and calculations made at the great Russian Ob- 

 servatory of Pulkowa, which show that such a change, at the 

 rate of about one foot per annum, has been going on through 

 the last quarter of a century, and are even believed in America 

 to be more accurate than the Greenwich observations. And 



Second, he must take up, and similarly destroy, the testimony 

 of the earlier Greenwich observations themselves, before these 

 last forty-seven years of his own computation began. 



Now those earlier Greenwich observations were so remarkable 

 for wliat they did indicate in their own time, that I may freely 

 mention now, seeing that all the parties are dead, that some- 

 where ahout 1836, Sir Thomas, then Mr. Maclear, at the Royal 

 Observatory, Cape of Good Hope, received a private letter from 

 Thonas Glanville Taylor, Honourable East India Company's 

 Astronomer at Madras — and earlier an assistant at the Royal 

 Observatory, Greenwich — stating his belief that the latitude of 

 the British National Observatory was continually decreasing ; 

 and he gave a list of latitudes, as determined by Greenwich 

 observati ins, so far back as they went, but condensed into three 

 epochs, to prove the point. 



The matter was kindly communicated to me by my then chief, 

 Sir Thomas Maclear, and was of course deemed interesting and 

 curious at the time ; but had quite gone to rest in my mind, until 

 twenty-nine years afterwards, when I fell across the same effect, 

 in the same direction and at nearly the same rate, but through a 

 longer period of time and to a much larger accumulated quan- 

 tity, at the Great Pyramid of Geezeh in Egypt. The datum for 

 the latitude of 4000 years ago, to compare with the present 

 observed latitude of the same spot — though exactly that which 

 the learned Dr. Hook desired so much, but in vain, to find 

 anywhere 200 years ago — is not perhaps so purely and perfectly 

 scientific as the high-class practical astronomers of our times 

 will always condescend to notice. But in the accompanying 

 feature of change of azimuth, so creditably brought to the front 

 by Mr. Flinders Petrie, there is a testimony of modern observa- 

 tion to ancient accuracy of so respectable a character — if I may 

 be allowed so to say — that it ought not to be entirely ignored ; 

 and it was first mentioned thus. 



While I was at the Great Pyramid in 1S65, and just after I 

 had there measured the azimuths of the entrance-passages of the 

 Great and Second Pyramids on successive evenings by reference 

 to the six-hour elongations of Polaris, there came a letter from 

 a retired civil engineer in Edinburgh, a man of long Batavian 

 experience in his day, and gifted with remarkable powers of 

 modern science and originality of mind, — in which letter lie was 

 pleased to run down all the presumed object of my work out 

 there on the Geezeh Hill. Especially too was he pungent on 

 the point that even the best of the ancients had not that triumph 

 of modern civilisation, "the manufacturing principle," in them ; 

 "for," said he, "they could not make two things alike." 



Whereupon I sent him the azimuths of the entrance-passages 

 of those two grand pyramids, so many hundred feet apart, and 

 pointed out, that, though they showed an error of azimuth for 

 modern date of nearly five minutes, yet the one pyramid ex- 

 hibited so very nearly the same identical quantity as the other, — 

 that they were, angularly, nearer together, or more exactly alike, 

 than were the two halves of one and the same azimuth circle I 

 was observing with. And yet that circle was by so celebrated a 

 maker of modem times as Troughton, and the instrument a 

 choice one specially made by him to be presented to the cele- 

 brated Prof. Playfair, by his admiring students in the University 

 of Edinburgh ; and by Playfair's executors, again, presented after 

 his death to the Royal Observatory, Edinburgh, where it is 

 still preserved in honour. C. PlAZZI-SMYTH 



15, Royal Terrace, Edinburgh, October 10 



The Sky-Glows 



In reply to Mr. Backhouse's question (p. 511) as to where the 

 context of Mr. Neison's remarks can be seen, I can only say 

 that I do not know. I came across the portion quoted relating to 

 these phenomena at the end of the Astronomer-Royal's Report 

 upon the Weather of 1S83. Like Mr. Backhouse, I have been on 

 the look-out for solar halos, or big rings round the sun as we call 

 them, for the last thirty years, more with a view to be prepared for 

 squalls, &c, when boating, than anything else. But for some years 

 there has been so much haze about the sun, and the weather has so 

 often cried " Wolf," so to speak, with no responding gale or squall, 

 that of late I have ceased to take much note of such warnings. 

 I may here mention that the rosy corona, when visible, as it so 

 often is now, can be well seen by looking towards the place of 

 the sun, but standing in the shadow of some high building ; or 

 at times by totally eclipsing the sun with a hat held between 

 him and the eye. 



As far back as January 1, 1S84, in a letter to the St. James s 

 Gazette, I ventured to predict that we had not seen the last of 

 what were then spoken of as the " Recent Sunsets " ; there was 

 a very remarkable after-glow ten days after this, reaching the 

 zenith, seen even in London. In the same letter of January I, 

 I suggested some increase in solar energy as the cause of these 

 phenomena. 



For some time, though feebler repetitions of the glows con- 

 tinued to be seen up to the end of March, there was nothing 

 strong enough in the way of colour worth noting. But from 

 what I continued to see in the shape of vapour, together with 

 that strange warm colour by day about the sun, I felt sure that 

 whatever might be the cause of these phenomena must- still be 

 going on, and in a short note dated April 12, I again spoke of 

 their probable early reappearance. A graphic account of these 

 after-glows, written by an observer at Smyrna, appeared in the 

 St. James s Gazette of February 25, in which he pointed out what 

 I have often since noticed, viz. that with excess of moisture all 

 colour disappears. 



This was at times very remarkable in the early part of July 

 this year, when we had some of the strangest white sunsets I 

 have ever seen. The sky around and above where the sun had 

 set, looking almost ceiling-like in its opacity, upon « hich soon 

 appeared numbers of weird small cloud forms, at times very 

 regular, like ripple-marks in sand, or the bones of some great 

 fish or saurian embedded on a slab of stone. 



Against these pale sunsets all buildings and trees told like 

 black velvet, while the clouds would rest almost stationary for a 

 long time. Years back such a sky would have betokened a 

 hurricane ; but evening after evening they were repeated, and 

 no storm of any importance followed. For many years past, but 

 notably during the summer of 1SS3, I had observed a steady 

 increase in a white luminous glare about the sun, so much so 

 that I wrote about it in the year 1S82 to my brother in India. 

 I was not therefore surprised altogether when as the sunsets 

 increased in colour, which they mostly do in autumn, that this 

 glare last winter was followed by something more than usual in 

 the way of colour ; and here I should like to say that, as far as 

 I have seen, and I have missed very few chances of watching 

 them, that though last winter twilights often increased up to a 

 certain time in strength, yet they did not exceed in duration the 

 time allotted to twilight in the almanacs. This letter is already 

 too long, but I cannot help asking, in conclusion, whether it 

 may not be possible that we have been all along muddling up 

 cause and effect, and that the eruption at Krakatoa, the recent 

 earthquakes and waves, as well as the strange atmospheric 

 phenomena, which are still about us, cannot all be traced to one 

 cause, viz. actual increase of sun power ? 



Southampton Robert Leslie 



This evening after sunset I noticed a column of yellowish 

 light over where the sun had set, and moving with the sun. I 

 have seen the same before. Can it be the zodiacal light ? T 

 have frequently noticed during the present year, while the sun 

 was much too high for any sunset colours, a pinkish colour in 

 the sky. This has been observed by others, but I do not know 

 whether it has been seen outside the British Islands. It must be 

 connected with the sunset-glows which several of your corre- 

 spoi dents have described. OSEPH John Murphy 



Belfast, October 12 



