272 



NATURE 



[January 17, 1895 



this plane ; and lee the mstioa be referred to S X, S Z, and a 

 line perpendicular to them as axes. Now in consequence of the 

 proper motions of the sun and the two stars, these lines will n')t 

 constitute a system of ates which are either fixed in space or 

 which move parallel to themselves ; consequently, if these lines 

 be taken as axes of reference the observed (or calculated) value 

 of the motion of rotation of any object will necessarily be 

 relative to these axes, and its absolute value cannot be deter- 

 mined without ascertaining the angular motion of the axes of 

 reference. But since the two stars have been specially selected 

 from amongst those whose proper motions have eluded de- 

 tection, the angular motions of the axes will be so small com- 

 pared with ordinar)' standards that the error caused by neglecting 

 them will lie within the limits of experimental error. If, for 

 example, we were to endeavour to calculate by the above 

 method, or some similar one. the ahs.^lule angular velocities of 

 the hands of a clock, or of a fly-wheel, the value which we should 

 thereby obtain would be as exact as the existing state of 

 mechanical and instrumental appliances admits. 



A series of observations extending over several thousand 

 years might of course reveal a proper motion of any two selected 

 stars ; but in the case of angular motions whose periods do not 

 extend much beyond a century, the above method leads to 

 results which are for most practical purposes exact. 



I am therefore disposed to think that all motions of rotation 

 of which our senses are capable of taking cognisance are 

 relative; but with the exception of certain astronomical motions 

 of very long periods, the absolute value of any motion of 

 rjtation which can be observed may be accurately determined 

 within the limits of experimental error. A. B. Basset. 



Fledborough Hall, Holyport, Berks. 



The gist of Mr. Love's long letter, on pp. 19S-9, seems to be 

 that since the specification of a force or a moti on depends upon 

 th; choice of axes, therefore the force or motion itself is 

 similarly dependent. A slight extension of the same principle 

 would make a velocity — say the velocity of light — depend upon 

 whether it was to be expressed in miles per second or in centi- 

 metres per hour ; and no extension at all is necessary to make 

 it depend on whether it is referred to Groombridge 1830, or to 

 some more quiescent body, if indeed the term quiescence may 

 b: allowed henceforth to have any meaning. 



Tycho Brahc is said to have held that there was only a question 

 of language between the Copernican and the Ptolemaic systems ; 

 bat, with the exception of a semi-ironical Church compromise 

 attributed to Descartes, he has been unfortunate in not finding 

 a disciple of importance until the present moment. 



It appears now to be equally true to say that the earth rises 

 to meet a stone, as to say that a stone falls to meet the earth ; 

 and considerations of energy are of no consequence ! 



I just want to add one word of my own on the subject, to 

 the effect that whereas the position of a body in an infinite 

 homogeneous stagnant ocean would be unmeaning and un- 

 specifiable, except by reference to boundaries or other bodies, 

 yet it does not follow that the rxlocily of a body through such 

 an ocean would be either unmeaning, unspccifiable, or un- 

 discoverable by experiment. It may be replied that such 

 motion would still be relative to something ; and to that I say 

 by all means, but it is not relative to other bodies such as are 

 competent to fix position, which is what Mr. Love is contend- 

 ing for. 



As to the other question, about absoluteness of rotation, I 

 shall be much interested in seeing what Prof. Grecnhill, and 

 with him Frofi. Mach and Karl Pearson, have to say on the 

 point Oliver J. Lodge. 



Liverpool, December 29, 1894. 



The Quarrying of Granite in India. 



At Bangalore, in Southern India, the quarrying of granite 

 slabs by meansof wood fire has been brought to such perfection, 

 that an account of the method may not be out of place. The 

 rock is a grey gneis-ose granite of very irregular composition 

 through unequ.il segregation of hornblende and the presence 

 of numerous felspathic veins. But it is otherwise very compact, 

 and forms solid masses uninterrupted by cr.icks for several 

 hundreds of feet. Only near the surface- the rock is found split 

 parallel to the surface. In one quarry there is thus, for in- 

 stance, a 4 feet thick horizontal layer of ralher weathered rock, 



NO. 131 6, VOL. 5 r ] 



underneath this another layer of fresh rock 3 feet thick ; but 

 below this the rock is entirely fresh, and not split. These 

 layers are probably due to the variations of temperature, daily 

 and seasonal. 



The undisturbed rock is quarried by means of fire, and it is 

 remarkable what large plates may be detached. I saw one 

 plate of 60 feet greatest length, and 40 feet greatest width, and 

 half a foot thickness. This thickness varied only one inch over 

 the greater part of the area. The whole plate had been de- 

 tached in one piece by means of wood-fire, .\fterwards the 

 plate was cut with blunt chisels into strips of 2ji feet width. 

 So easily are these strips and slabs obtained, that it is quite 

 common to see palisades of them used instead of boundary 

 walls, and also to see them used as posts for huts, for telegraphs, 

 and for railings and posts in gardens. 



In one case, I observed the operation of burning over an area. 

 A narrow line of wood-fire, perhaps 7 feet long, was gradually 

 elongated, and at the same time moved forward over the 

 tolerably even surface of solid rock. The line of fire was pro- 

 duced by dry logs of light wood, which were left burning in 

 their position until strokes with a hammer indicated that the 

 rock in front of the fire had become detached from the main mass 

 underneath. The burning wood was then pushed forward a few 

 inches, and left until the hammer again indicated that the slit 

 had extended. Thus the fire w,-is moved on, and at the same 

 time the length of the line of fire was increased and made to be 

 convex on the side of the fresh rock. The maximum length 

 of the arc amounted to about 25 feet. It yvas only on this ad- 

 vancing line of fire that any heating took place, the portion 

 which had been traversed being left to itself. This latter 

 portion was covered with the ashes left by the wood, and with 

 thin splinters which had been burst ofl". These splinters were 

 only of about ith inch thickness, and a few inches across. 

 They were quite independent of the general splitting of the 

 rock, which was all the time going on at a depth of 

 about five inches from the surface. The burning lasted 

 eight hours, and the line of fire advanced at the average 

 rate of nearly 6 feet an hour. The area actually passed over by 

 the line of fire was 460 square feel, but as the cr.\ck extended 

 about 3 feet on either side beyond the fire, the area of the entire 

 slab which was set free measured about 740 squ.ire feet. All 

 this was done with, may be, about 15 cwt. of wood. Taking 

 the average thickness of the stone at 5 inches, and its 

 specific gravity as 2 62, the result is 30 lbs. of stone quarried with 

 I lb. of wood. 



The old quarries have sloping sides formed of steps left by 

 each successively split plate, each new plate extending to within 

 about 2 feet of the step left by the preceding plate. Many plates 

 are taken out in an inclined position, and as the directions of in- 

 clination dilTer, it follows that the action of the fire is quite 

 independent of the original surface of the rock, and also of the 

 direction of lamination and of the numerous veins in the rock. 

 The action of the fire is thus very similar to that action which 

 produces dykes and faults 0:1 a large scale, more or less 

 independent of the nature of the rocks which are passed 

 through. 



The great uniformity of the thickness of the slabs formed by 

 the above process is probably due to a regulating influence of 

 the pre-existing crack. When the action of the fire is some- 

 what slower, it takes longer for the heat to penetrate down to 

 the crack ; when the action is quicker, there will be enough ex- 

 pansion produced in the upper layers, and the lower layers 

 transmit the tension to the plane of the crack. IV-rhap-i it will 

 be possible some day to measure the temperature of the heated 

 rock, when a certain agreement ought to be found between the 

 tensile strength of the rock and the strain which the expansion 

 by the heat produces in the so-far elastic rock. 



Bangalore, December 19, 1894. II. \V.\RrH. 



Storm Statistics at Bidston. 



The Liverpool Observatory, erected at Bidston, on the 

 Cheshire side of the estuary of the Mersey, stands on a 

 slight eminence about 200 feet above the sca-lcvel. The ascent 

 is tolerably steep on each side except from the south, and with 

 the Irish Sea on the north, and Ihc rivers Mersey and Dee on 

 the east and west sides respectively, there is nothing to obstruct 

 or diminish Ihc force of a passing slorm. .Self-recording ane- 

 mometers of the Robinson and Osier types have been in position 

 since 1SO7, and it is from the records of these instruments that 



