JuLT 10, 1885.] 



♦ KNOW^LEDGE ♦ 



INFINITE DIVISIBILITY. 



[1804]— Does not the difficulty concerning infinite divisibility 

 arise from the confounding of two separate questions, of which the 

 one is concerned with natural history or physics, and the other with 

 either formal logic or metaphysics ? 



The question whether or not there is a limit to the divisibility of 

 matter is surely a question of physics. Matter may be composed 

 of small portions capable of resisting the disintegrating action of 

 any natural process whatever. These portions will then be, physi- 

 cally speaking, indivisible; and we must then say that there is a 

 limit to the divisibility of matter. 



Whether or not this is the characteristic of matter is a question 

 of Bcienoe, and must bo settled, if settled at all, not by any intuitive 

 intellectual effort, but by actual experiment. 



The other question is not a physical but a metaphysical question. 

 In this sense, "infinite divieibility " is no longer concerned with 

 the divisibility of any substance by any force, but is concerned 

 with the divisibility of a mental abstraction, and, therefore, has no 

 more to do with the divisibility of an atom of matter than the 

 triangles and circles of the geometer have to do with those of the 

 brassfoundcr. 



If these considerations are applied to the example given by 

 " U.allyardB" (1747) of the disk and its centre, it will bo clear, I 

 think, 'that the difficulty does arise from the confusion to which I 

 have referred. 



The diak of which he speaks and thinks Ib a piece of metal, card- 

 board, or other substance ; but the centre flf which he speaks and 

 thinks is the geometrical centre of a geometrical circle, and not a 

 material atom. 



Descartes rightly taught that one of the requisite precautions for 

 the discovery of truth is to divide a complex question into its com- 

 ponents. Let us, therefore, begin by separating the empirical 

 question as to the structure of matter from the metempirical ques- 

 tions of ideal geometry. 



I believe this problem has been discussed by Mr. G. 11. Lowes in 

 " Problems of Life and Mind," and also by Prof. Clifford in one of 

 his published " Lectures and Essays " ; but I have not the books to 

 refer to. M. B. 



GHAVITATION. 



[1805]—" No two gases of different composition can remain in 

 contact with each other without mutually intermingling or diffusing 



themselves through each other But for this diffusion, and 



the fact that it overpowers gravitation, we could not live upon the 

 earth. " — KivowLEncE, p. 539. 



May I not claim tliis as another influence counteracting gravita- 

 tion as a universal law? By it, carbonic acid gas sJtould always 

 be lowest ; which in practice it is not ; yet no chemical mixture 

 prevents its obeying the law. Ualltaed.s. 



EYEBROWS 



11- glad if any ri'iido 



than we " foreign barbarians," and to believe that the inexorable 

 law of Progress will compel us to follow in hia "celestial" foot- 

 steps? One feels inchned to say, " God forbid." E.T. C. W. 



DISINTEGRATION OF THE WEALDEN SANDSTONE. 



[1808]— A correspondent (letter 1779), in alluding to certiuB 

 markings on rocks at Tunbridge Wells, uses these words : " They 

 must have been abraded in almost historic times." This sandstone 

 formation, like all the Wealden strata, is a fresh-water deposit, 

 composed of quartz, more or less comminuted, and fine clay (loam) 

 in varying proportions, held together by a solution of iron. It is 

 not affected by frost, but the solvent power of rain-water in time 

 finds out its softer parts, and washes them away, leaving the 

 liarder or insoluble parts standing up in relief as irregular ridges, 

 hence the honeycomb markings, or pits, to which your corre- 

 spondent alludes. 



The time required to produce this honeycombing under the ordi- 

 nary condition of the rock is, I think, far longer than the three 

 thousand years or so constituting the historic period. I have 

 formed this opinion on the following grounds, made from personal 



Trinity Church, Tunbridge Wells, was built about sixty yeara 

 ago of this stone, dug from quarries within a mile of it ; the church 

 is unprotected from the south and west, yet the tool-markings 

 upon the stones are as sharp and well-defined as if made yesterday. 

 The oldest squared-stone erections that I know built of it date from 

 about 1350; take Bodiam Castle and Etchingham Church as 

 examples ; they show little or no sign of weather wearing, and the 

 scanty tool-marks of the workmen, made more than 500 years, are 

 still visible. The present appearance of this stratum, exposed as 

 rocks and cliffs at Tunbridge Wells and in East Sussex generally, is 

 due to two causes, the primary one being the enormous denudation 

 which followed in comparatively recent geological times its up- 

 heaval from great depths, the second and cluef cause being sub- 

 aerial denudation. The cracks and crevices, from the fraction of an 

 inch in width to any number of feet, are due entirely to its eleva- 

 tions with all the Tertiary deposits upon it. These have all been 

 denuded, except a bit or two on the south coast. The town of Sea- 

 ford is buUt on one of the remnants of the Tertiaries ; the horizontal 

 sandstone-floor could not stand the pressure upwards without 

 breaking, hence these fractures. ' c!„.„n 



John Shabp. 



FORM OF THE HEADS OF PROJECTILES. 



;nd3 the following foi 



l_>, --I'l-jiiisiiig eyebrows to 

 ■d the whole forehead, are 

 e advanced state of evoluti 



myself to clear a garden 



