JuLT 3, 1885.] 



KNOW^LEDGE 



wait for proy, that it was with great difficulty detected. I enclose 

 a ekotch of Thomisits abbreviafuis, which may perhaps enable 

 " llallyards" to decide whether the determinatiou is correct. 



E. A. Butler. 



THE PBEVENTION OF COLLIERY EXPLOSIOXS. 



tnptedy Can any 

 installation of the 

 a recent article ir 



[1792]— How many 

 without preventive meuHures ueiug a 

 expert inform me what would be the 

 electric light in mines ? Herr Juliu 



the Fortnightly on " Electricity," has provea mat tuo mme-ligntmf; 

 question by electricity has been brought within the range of 

 praotioal possibilities; and I myself, two years ago, heard Professor 

 Tyndall confess it could be managed, and these terrible disasters 

 averted, if it were not for the expense. Surely some association or 

 society might be formed to collect funds for such a purpose. The 

 British public is ever ready to come forward upon charitable pre- 

 texts, and if once it was fully understood that the illumination of 

 mines by electricity was not an impossibility, subscriptions would 

 be forthcoming. Science, who never turns her back upon us when 

 we need her aid, can help our poor miners now if man will let her. 



ROCKS OP CHARNWOOD. 



[1793]— I am pleased to know that my article on Chamwood 

 has led Jlr. Fletcher and his friends to study the remarkable rocks 

 of that region. The quarry which he describes in Brazil Wood is 

 clearly the one to which I referred, and I am glad that he saw 

 clear evidence there of the intrusion of the granitic into the slaty 

 rocks. If ho visits the spot again, I hope he will search for the 

 garnets which have been plentifully developed in the altered slate. 

 I found them most abundantly in the corner farthest from the gate. 

 They are dark — nearly black — in colour, and vary in size from 

 microscopic dimensions to about the eighth of au inch in diameter. 



The pebbles and gravel lying on the top of Mountsorrel hill- 

 some 200 feet above the level of the Soar Valley— probably mark 

 the stage of depression which followed the deposit in England of 

 the great chalky boulder clay — itself the moraine of a mighty 

 glacier. England went down, perhaps, 2,000 feet in the west and 

 south, but much less in Leicestershire; perhaps not more than 

 -100 feet. Still, this change would be quite suflBcient to submerge 

 most of the Charnwood hills, including Mountsorrel, and during 

 the washing and redistribution of the surface boulder clay which 

 then took place, the pebbles now forming a thin covering to the 

 hill-top may have received their rounding. 



But Mr. Fletcher states that he found bones and fragments of 

 pottery in tlie loiter part of the stratum containing the pebbles. 

 This 1 consider to be owing to the fact that the stones have been 

 moved partly down the hill by rain, &c., since the time of their 

 original deposition. The real summit of Mountsorrel — long since 

 quarried away — was much higher than the part which now remains. 

 All such exposed summits get washed bare, and the tU-i-i'is is 

 pushed down the slopes. I may add that a fine flint javelin-head 

 which I f u d 1 probably a corresj ending position to the bones, 

 >to lu lb"t) would possibly be coeval with them, and that bones, 

 pottery and all are I thouU cci s der, i-eferablo to a period some- 

 wheie ab t tl 1 f tl e K u an occupation of this country. 





of 



L the 



1 I I 1 el| n settling th 



1 1 k t would be a good thing if local workers 



more fre [uently with short, condensed 



ot 1 e under their observation. It is certain 



that in flail teresting facts arc lost to the world of 



c cncc for tl o gl olsor^ed they are not recorded. 



W. Jei(o.me Uaiuuson. 



TWO-SPEED GEARINCx. 

 [1704]— In reply to " W. J.," Bown's two-speed gearing performs 

 excellently, provided it is so adapted to a tricyclo that it can bo 

 changed from power to speed easily. John BR0WNiN(i. 



A PARADOX. 



[1795]- Your rovrc.^pondont " Culrford " (1772) ,u-opoun<ls lu. 



r great -groat-great-grand- 

 .t help intermarrying as I 



3 wife's grandfather. 



[1790]— The solution of the rather curious paradox wWch occurs 

 upon page 533 is to be found in the following simple facts : — 

 Although every single individual in ordinary parlance is said to 

 possess two grandfathers, four great-grandfathers, <ic., these 

 various antecedents are at once, grandfathers, &.C., to many other 

 individuals. 



Moreover, when marriage is contracted between members of the 

 same family, as is often the case among certain African tribes, it 

 occasionally happens that a person has but one grandfather, his 

 father's father and his mother's father being one and the same. 



A glance at the annexed diagram will show at once ho^ 

 matter stands ; the dot.s represent individuals, and those a 

 of each angle indicate the parents of the person foi 



the 



z ther 



? dowi 



From this 



that if we allot to any individual in the lower line (A for example) 

 his common share of ancestors, he will posses a grandfather on hia 

 mother's side and another on his father's side (apparently two, 

 but in reality only one) ; the fathers of these, and of their wives, 

 make four great-grandfathers (still represented by one) who, with 

 their wives, are the offspring of eight great-great-grandfathers (the 

 complete eight, as a matter of fact, being a single individual of the 

 first pair). Again, ten boys, each having a father, should make 

 ten fathers in all, but if the boys are brothers there is only one 

 father. All humanity must be more or less related, and the 

 evident reason which your correspondent requires why the popu- 

 lation increases instead of decreasing, is because in almost every 

 case a grandfather has more grandchildren than a single grandchild 

 has grandfathers. Alex. Mackie. 



[Solutions are also sent by " Scotus," George Falkner, F. W. H., 

 A-c.-En.] 



SYMMETRY. 



ins of taste frequently a))] 

 it in using the word " .-vi 

 th balance ? Surely he is not. Nev, 

 one in this misuse of the word ; it .>■ 

 1 journals devoted to art subjects, i: 

 not symmetry. Symmetry, accordin] 

 armony of proportion — the proportion 

 hole together. A work either of Nati 

 id without being symmetrioul. As t 



But 



rs of t, 

 ,s the ei 



it B 

 1 to be 8 



can be clearly 



LETTERS RECEIVED A 

 W. C. Penny was horribly shock 



