388 



NA TURE 



\August 25, 1887 



OUR BOOK SHELF. 



Annals of the Astronomical Observatory of Harvard 

 College. Edward C. Pickering, Director. Vol. xvii. 

 (Cambridge : John Wilson and Son, 1887.) 



This volume of the Annals of the Harvard College Observa- 

 tory contains the description and theory of the instrument 

 invented by Mr. S. C. Chandler, and called by him the 

 almucantar, as well as the reduction and discussion of a 

 series of observations made with it at the Observatory in 

 1884 and 1885. The instrument consists of a telescope 

 mounted upon a base that floats in mercury, and the 

 observation consists in noting the time of transit of a star 

 across an almucantaral (or horizontal) circle, the particular 

 horizontal circle which the inventor has found most con- 

 venient being that passing through the Pole, which he has 

 called the "co-latitude" circle. If, therefore, the tele- 

 scope be clamped at the given altitude, " the sight-line 

 will mark accurately in the heavens a horizontal circle : 

 and the transits of stars, as they rise or fall over this 

 circle in different azimuths, will furnish the means of 

 determining instrumental and clock corrections, the lati- 

 tude, or right ascensions and declinations." Mr. Chandler 

 beheves that an instrument on the almucantar principle 

 is capable of giving results more free from both accidental 

 and systematic errors than those obtained from a meridian 

 circle, and certainly the discussion of his observations 

 contained in the volume before us goes far to justify such 

 a belief. The probable accidental error of a single 

 observation in zenith distance is ± d'-\o\, whilst for stars 

 north of 60° declination it is as small as ± o"-379 ; the 

 probable accidental errors of the clock corrections from a 

 complete transit (including the residuals for Polar stars) 

 are ± o-047s. and ± o-o43s. for two observers. And these 

 results have been obtained, it must be remembered, with 

 a telescope of only 4 inches aperture and less than 44 

 inches focus. The chief advantage of the system is, how- 

 ever, that it gives measurements of both co-ordinates of a 

 star which are absolutely free from the effects of flexure, 

 and also of refraction as far as it depends on zenith 

 distance. The almucantar certainly appears to be a valu- 

 able addition to our means of attacking difficult problems 

 of practical astronomy. 



The Distribution of Rain over the British Isles during 

 the Year 1886. Compiled by G. J. Symons, F.R.S. 

 (London : E. Stanford, 1887.) 



Mr. Symons explains that the delay in the appearance 

 of this volume is due chiefly to the exceptional character 

 of many of the phenomena of the year 1886, and partly 

 to some observers not having had sufficient health, or 

 courage, or interest in their records, to induce them to 

 face the snowstorms of March i and December 26. 

 The volume contains, besides articles upon various 

 branches of rainfall work, the results of observations 

 made at nearly 2500 stations in Great Britain and Ire- 

 land. In the various sections the compiler has brought 

 together an immense mass of information, and he has 

 taken great pains to present his facts clearly. There are 

 several illustrations, in one of which he shows the fluctua- 

 tions of annual rainfall from the year 1726 to 1886. 



LETTERS TO THE EDITOR. 



\The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 take to return, or to correspond with the writers of, 

 rejected manuscripts. IVo notice is taken of anonymous 

 communications. 



Slate Ripples on Skiddaw High Man, 



The slate ripples on Skiddaw are not, so far as I am aware, 

 mentioned by writers on the Lake District, geological or other - 



wise. Their peculiar character puzzled me so much, af 

 noticing them on Saturday, July 23, that I visited the spot agi 

 on the 30th to see whether the origin which suggested itself 

 me was probable. 



Following the pathway from Keswick, you pass through 

 small gate a little way up the final ascent, from the dip betwe 

 Skiddaw Low Man and High Man. Turning to the left alo 

 the wire fence, one comes, where it ends, to the best-develop 

 of these peculiar ripple marks ; but they extend upwards frc 

 here on the left (south) side of the pathway until you are m( 

 than half-way up to the first cairn. On the right (north) si 

 the ripples begin later, extend higher, but are less distin 

 They cease, apparently, simply from want of the clay foundatic 

 which is an essential feature in their development. 



The rippled areas are patches of bare clay or soil, from a f 

 yards to half an acre or so in extent, coated with a thin layer 

 the slates, which elsewhere form the cap of Skiddaw High Mj 

 The slate fragments, however, instead of being confused, fo 

 more or less regular lines, generally running norlh-west a 

 south-east, but varying towards north and south or east and we 

 when the patches are small and longest in these directions. T 

 greater the slope the greater appears to be the average size of f 

 slates. The larger fragments average a foot by four or fi 

 inches, always lying lengthwise along the lines, which are sev 

 or eight inches apart. The clay is washed out beneath t 

 stones, which therefore do not rise above the general level. T 

 clayey intervals have numerous smaller bits of slate, and i 

 scored at right angles to the lines by the action of rain a 

 wind on these. Of course there are always loose fragments r 

 on the chief lines. 



Obviously the slates are arranged by the wind, apparen 

 without much aid from water, as the slopes would not let it c 

 lect. But it would be very interesting to have a compl 

 explanation of the lines. 



A suggestion, largely confirmed by my second visit, may 

 any rate help to solve the point, even if it is inadequate by its« 

 The hurricane force of Skiddaw storms, mostly from the sou 

 west, no doubt drives before it the loose slates, sliding over t 

 surface of the slates below. On reaching a bare patch, the frc 

 edges of the slates are stopped by the clay. Finally a sudd 

 gust tilts them over. Thus a first line is formed. RIore sla 

 slide, or are tilted over, upon the first layer, which have mer 

 while worked down to the general level by rain action. T 

 second set slide over the first set and are in their turn tilted o\ 

 on reaching the far side. Thus a second line is formed, and t 

 rest follow in the same way. On slopes larger fragments j 

 moved than on the level ; hence such are there found in t 

 lines. In small areas, with their long axes not perpendicular 

 the prevailing winds, the general direction is modified by t 

 natural position (according to the explanation here suggested) 

 the first line. 



There was a moderate gale on my first visit, and only a s 

 breeze on my second, neither enough to move stones. But 

 the latter occasion, hearing a strange hissing noise, I looked 

 and saw a violent, eddy, 20 or 30 yards across, whirling sm 

 slates 20 to 40 feet into the air. This advanced from the sou 

 west at the rate of 8 or 10 miles an hour, coming so close tl 

 some of the fragments fell around and on me. 



Probably the lines are stationary, although the stones m 

 pass from one to another. To test this, if possible, I took 

 on the second occasion seven small Permian sandstone pebb 

 from the shore and placed them a foot or less apart on the wi^ 

 war^edge of a conspicuous line, sheltering each behind a nam 

 slate, hammered firmly into the ground. I am not likely to 

 up again, but should any of your readers be on the spot a f 

 months hence they might find the line in question by ascendi 

 the path until the line of the Helvellyn range is above Skidd 

 Low Man by about the breadth of a pencil held at arm's leng 

 The line lies twenty-seven paces to the left of the path. 



I might mention that the thermometer was at 45° on the I 

 about half-past one or two, when the sun was clouded. So 

 after four, at Crosthwaite, the same thermometer was at 63" 

 the shade. J. Edmund Clark 



August 2. 



Dr. Klein and " Photography of Bacteria." 



Although I feel indebted to Dr. Klein for his appre^ 

 of my work as expressed in his review in Nature of Augus 

 (P- 317)) still I must ask him to allow me to correct a sti, 



Ji 



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