526 



NATURE 



{Oct. 12, 1876 



Mallock, as due (in Mr. Mallock's case) to ««(/i?r-refraction of 

 rays (as in my case it certainly is due to ^z'^^-refraction), his own 

 experience furnishes a good connecting-link between the "two 

 different, though allied, phenomena." It would be well, how- 

 ever, in order to avoid all uncertainty, that we should know the 

 result, in Mr. Mallock's case, of experiments with an obstacle 

 advanced in front of the eye from a given direction. The ex- 

 periment with concave or convex spectacles is not quite satis- 

 factory, because it involves a breach of continuity in the observa- 

 tion of the phenomenon. 



In concluding that I am " evidently short-sighted," Mr. Back- 

 house attributes to the whole lens a fault which really belongs 

 only to certain radial portions of the marginal region of the lens. 

 In daylight I see distant objects sharply defined, and that with- 

 out excessive contraction of the pupil. It is at night, when the 

 pupil is largely dilated and the mar spinal part of the lens 

 becomes exposed to incident rays, that I see radiance around a 

 distant lamp. 



These phenomena being necessarily personal to each observer, 

 not admitting of observation by one person for another, and 

 evidently presenting wide differences, it would be interesting to 

 collect and tabulate the facts as described by a number of com- 

 petent observers. I would suggest that the initiator of this 

 correspondence (Mr. A. Mallock), or some other person, with 

 the approval of the editor of Nature, should receive and tabu- 

 late such facts as may be communicated on this subject, with a 

 view to the publication of the results in a future number of 

 Nature. Hubert Airy 



Blackheath, October 3 



An Intra-Mercurial Planet 



If the phenomenon seen' by the Hon. F. A. R. Russell was 

 really a transit of this planet, Hofrath Schwabe must have very 

 narrowly escaped witnessing it, for on turning to his MSS. I 

 found the following observation for the date in question : — 



•' i860, Jan. 29, 9m. (8. 1 1 A.M., G.M.T.). 



" Nur die Hauptflecken von 10 deutlich dem Austritte nahe, 

 II undeutlich, 12 u. 13 nicht wesentlich verandert." 



The numbers refer to the drawing of sun-spots made on the 

 preceding day, indicating also the order in which the spots 

 have appeared since the commencement of the year. No. 10 is 

 a group of spots near the limb. No. 1 1 a group of very small 

 spots also close to the limb, whilst 12 and 13 are clusters of 

 large spots both of sufficient magnitude to be visible to the 

 naked eye through a fog. 



Unfortunately the Photoheliograph was not at work on that 

 day, nor did Carrington make any observations, the sky being 

 cloudy. G. M. Whipple 



Kew Observatory, October 7 



Inequality of the Semi-Diurnal Oscillations of Baro- 

 metric Pressure 



Will you oblige me by publishing the following corrections 

 of certain of the formulae in my paper on the Inequality of the 

 Semi-Diurnal Oscillations of Barometric Pressure, in Nature, 

 vol. xiv. p. 316 ? I regret that the distance of my place of resi- 

 dence has prevented my sending you an earlier notice of the 

 errors. 



Formula (2) should stand thus — 



P T 



" wherein p is the density of air at standard pressure P and tem- 

 perature To, &c." 



The same symbol P should be substituted for P in the next 

 formula, and the explanation should run — 



"where s is the hypothetical density of water vapour at P and 

 7^, and \ its latent heat at temperature 7. Substituting for s 

 its approximate equivalent -| p, 



r= VlptZ^K." 

 '^ P T 



Henry F. Blanford 

 Meteorological Office, Calcutta, September 5 



Miniature Physical Geology 



The occurrence of miniature earth-pillars (vol. xiv. p. 423) 

 is by no means unusual even in our own country. 



I noticed some excellent examples some years ago in the 



neighbourhood of Halifax. From a steep exposure of alter- 

 nating strata of sandstone and shales, the sandstone stood out in 

 broad ledges which received on their upper surface the dJbris 

 from the weathering shale, consisting of mud and plate-like frag- 

 ments of the shale itself. Und«r ilie action of the rain this 

 debris had been carved out into perfect pillar?, each capped with 

 its plate of shale, and with a numerous progeny of smaller pil- 

 lars clustering round it, each also with its protecting roof of 

 jutting shale. 



Near the Mumbles (Swansea) I visited a limestone quarry at 

 the foot of which lay a talus of soft earth embedding a number 

 of fragments of limestone. Here not only were large earth- 

 pillars from two to four inches high, and in every detail of form 

 resembling those of the Tyrol, to be seen sculptured from the 

 talus, but a heavy shower of rain falling at the time was actually 

 at work producing fresh columns and enlarging the old ones. 

 I had with me at the time, by good fortune, a party of some 

 forty students, and was pleased beyond measure to be able to 

 point out to them these beautiful pillars and the process of their 

 growth. So perfect were they that one gentleman more enter- 

 prising than tl;e rest wished to transport one fine group to the safe 

 keeping of a glass case. 



But the most striking examples of earth-pillars I have seen 

 anywhere occur in this neighbourhood. The trias, which 

 here 'frequently consists of a breccia of hard sub-angular frag- 

 ments of various kinds of rocks embedded in a red sandy marl, 

 is in many localities cut through by the roads, and thus exposed 

 in almost vertical faces of considerable length on the side of the 

 roadway. These faces have very generally been carved out into 

 earth-pillars, which, whilst resembling in all else the Botzen 

 pillars, differ from them in remaining attached vertically to the 

 parent rock by one face, and thus are free on three sides only. This 

 ornamentation of the rock-faces in high relief maybe seen contin- 

 uously for many yard', I should think for hundreds, and it is per- 

 manent from year to year. No one walking from Dawl'.sh to 

 Little Haldon can fail to be struck with its singular appearance, 

 and it is especially well exhibited on the right hand bank of the 

 road skirting the north- east side of Luscombe grounds. The 

 ordinary earth-pillars, free on all sides, may also be occasionally 

 noticed in great perfection. After last year's heavy rains I saw 

 several measuring 3 inches high and 2 inches broad at the 

 summit : in one case the capping was not of stone, bat a piece 

 of growing moss, which had become detached from a mossy 

 bank by a landslip on a small scale. W. J. Sollas 



Dawlish, Devons 



The Claywater and Meno Meteorites 



The analyses of these remarkable bodies by Dr. J. Lawrence 

 Smith, as given in the American Journal of Science for September, 

 1876, suggest a new and interesting inquiry in astro-meteorology. 

 These analyses gave the following results : — 



" In regarding the above comparative statement of the com- 

 position of these meteorites," says Dr. Smith, "it will be seen 

 that the compositions of the two as made out by me do not 



