March 15, 1894] 



NA TURE 



469 



Pin-wells and rag-bushes are still frequented, and on the night 

 before emigrating people will sleep in the open, beside one of ! 

 the holy wells, in order that they may have good f .rtune in ihe I 

 country to which they are going. There is a firm belief in the 

 power of the Evil Eye, and on certain days that are considered 

 unlucky, even burials are avoided. 



The antiquities of the Aran Islands are numerous and varied, 

 but have never yet been systematically described ; and the authors 

 urge upon the Irish Academy the desirability of its undertaking 

 a detailed survey of them. 



No opinion is expressed as to what race or races the Aranites 

 belong, but it is argued that they cannot be Firboigs, if the 

 latter are correctly described as "small, dark-haired, and 

 swarthy." 



A short bibliography is given at the end of the paper, and a 

 few photographs, taken by Prof. Haddon, give a general idea of 

 the appearance of the people. 



ELECTRICAL S ANITA TION. 



A PRACTICAL application of electricity to sanitation has 

 "^ recently been made. Two systems have been tested upon 

 a very considerable scale, in both of which the electrolytic 

 action of the current has been utilised. 



The two methods at present before the public are Mr. William 

 Webster's, which is being carried out by the Electrical Purifi- 

 cation Association (Limited), and that ascribed to Mr. Eugene 

 i lermite, and worked by him in conjunction with Messrs. 

 Paterson and Cooper. 



As has occurred so frequently before, both these inventors 

 appear to have conceived the same idea about the same time. 

 Each of them took out three patents in the year 1S87, but 

 though each had the same object in view, and although in 

 their early patents ihey seemed -almost to be running on the same 

 rather than on parallel lines, their recent practice is quite 

 distinct. 



Mr. Webster treats the sewage directly. He places parallel 

 iron electrodes within a conduit or shoot, through which the 

 sewage is passed, the electrodes being alternately connected 

 with the positive and negative poles of a dynamo. The nascent 

 ammonia thus evolved at the negative electrode' produces an 

 alkaline reactir n, which effects the precipitation of the solid 

 suspended matter, while at the positive pole nascent oxygen 

 and chlorine are evolved, producing an acid reaction, whereby 

 the organic impurities held in suspension or solution are readily 

 decomposed and purified. 



This system has been tested on a large scale, both at Cross- 

 ness and at Salford, The amount of sludge formed is said to 

 be smaller than in any precipitation process, and the effluent so 

 pure as not to require further treatment by filtration. The pro- 

 cess has been reported on in the most favourable manner, 

 as regards the chemical tests of the efliuent, and the ease and 

 uniformity with which the results are obtained. 



Mr. Hermite's system consists in the treatment of sea water 

 or other chloride solutions by electrolysis. The water thus 

 electrolysed in reservoirs is conducted as a disinfecting 

 liquid by suitable pipes to places requiring disinfection, where 

 it IS stored in cisterns and used in place of ordinary water. 

 The system has been experimentally tested at Havre, Lorient, 

 Brest, and Nice, and has been reported upon most favourably 

 in every case. It is now being tried at Worthing, where an 

 installation has been set up under the auspices of the Mayor and 

 corporation. As in the previous system, an oxygenated com- 

 pound of chlorine is held to be produced, which burns up the 

 sewage matter, and absolutely destroys all microbes. 



Several questions have to be considered from a scientific 

 and practical point of view, in connection with both these inven- 

 tions, before their general application can be effected. The scien- 

 tific view of the subject, after all, resolves itself into the answer 

 to a single question : Is the process quite trustworthy to remove 

 the maximum of organic matter from the sewage, and thoroughly 

 sterilise it ? As regards the practical point of view, the re- 

 moval and utilisation of the sludge will have to be faced, in the 

 first process rtferred to ; whilst in the second, in which sludge 

 is said not to be produced, a second water supply to houses, 

 and the chemical action of this disinfecting water upon the 

 pipes, tubes, and reservoirs through which it has to pass, will 

 have to be very fully considered before the system can be 

 adopted. 



hO. 1272, VOL. 49] 



ON HOMOGENEOUS DIVISION OF SPACE} 



H. 



g 10. IVTOW, suppose any one pair of the tetrahedrons to be 

 taken away from their positions in the primitive paral- 

 lelepiped, and, by purely translational motion, to be brought 

 into position with their edges of lergth qd coincident, and the 

 same to be done for each of the other two pairs. The sum of the 

 six angles at the coincident edges being two right angles, the 

 plane laces at the common edge will fit together, and the condition 

 of parallelism in the motion of each pair fixes the order in which 

 the three pairs come together in the new position, and shows us 

 that in this position the three pairs form a parallelepiped essen- 

 tially different from the primitive parallelepiped, provided that, 

 for simplicity in our present considerations, we suppose each 

 tetrahedron to be wholly sjalene, that is to say, the seven lengths 

 found amongst the eJges to be all unequal. Next shift the tetra- 

 hedrons to bring the edges qe into coincidence, and ntxt again 

 to bring the edges of into coincidence. Thus, including the 

 primitive parallelepiped, we can make four different parallele- 

 pipeds in each of which six of the tetrahedrons have a common 

 edge. 



§ II. Now take the two pairs of tetrahedrons having edges of 

 length equal to n.\, and put them together with these edges 

 coincident Thus we have a scalene octahedron. The remain- 

 ing pair of tetrahedrons placed on a pair of its parallel faces 

 complete a parallelepiped. Siinilarly two other parallelepipeds 

 may be made by putting together the pairs that have edges of 

 lengths equal to QB and QC respectively with those edges co- 

 incident, and finishmg in each case with the remaining pair of 

 tetrahedrons. The three parallelepipeds thus found are 

 essentially different from one another, and from the four of 

 § 10 ; and thus we have the seven parallelepipeds fulfilling the 

 statement of § 9. Each of the seven parallelepipeds corresponds 

 to one and the same homogeneous distribution of points. 



§ 12. Going back to § 4, we see that, by the rule there given, 

 we find four different ways of passing to thetetrakaidekahedron 

 from any one chosen parallelepiped of a homogeneous assem- 

 blage. The four different cellular systems thus found involve 

 four different sets of seven pairs of neighbours for each point. 

 In erch of these there are four pairs of neighbours in rows 

 parallel to the three quartets of edges of the parallelepiped and 

 to the chosen body-diagonal ; and the other three pairs of 

 neighbours are in three rows parallel to the face-diagonals which 

 meet in the chosen body-diagonal. The second (§ 11) of the 

 two modes of putting together tetrahedrons to form a parallel- 

 epiped which we have been considering suggests a second mode 

 of dividing our primitive parallelepiped, in which we should first 

 truncate two opposite corners and then divide the octahedron 

 which is left, by two planes through one or other of its three 

 diagonals. The six tetrahedrons obtained by any one of the 

 twelve ways of effecting this second mode of division give, by 

 their twenty-four corners, the twenty-four corners of a space- 

 filling tetrakaidekaliedronal cell, by which our fundamental 

 problem is solved. But every solution thus obtainable is clearly 

 obtainable by the simpler rule of § 4, commencing with some 

 one of the infinite number of primitive parallelepipeds which 

 we may take as representative of any homogeneous distribution 

 of points. 



§ 13. The communication is illustrated by a model showing 

 the six tetrahedrons derived by the rule 4 from a symmetrical 

 kind of primitive parallelepiped, being a rhombohedron of 

 which the axial-diagonal is equal in length to each of the edges. 

 The homogeneous distribution of points corresponding to this 

 form of parallelepiped is the well known one in which every 

 point is surrounded by eight others at the corners of a cube of 

 which it is the centre ; or, if we like to look at it so, two simple 

 cubical distributions of single points, each point of one distri- 

 bution being at the centre ol a cube of poin'.s of the other. To 

 understand the tactics of the single homogeneous assemblage 

 constituted by these two cubic assemblages, let p be a point of 

 one of the cubic assemblages, and Q any one of its four nearest 

 neighbours of the other assemblage. is at the centre of a 

 cube of which P is at one corner. Let pd, pe, pf be three con- 

 terminous edges of this cube so that A, B, c are points of the 

 first assem''age nearest to p. Again is a corner of a cube of 

 which p i .he centre ; and if qa., qb, qc are three conterminous 

 edges of tnis cube, D, E, F are points of the second assemblage 



' A paper react befjre the Royal Society on January 18, by Lord Kelvin, 

 P.R.S. (Cuntinued from p. 448.) 



