Dec. 2, 1881.] 



KNOWL.EDGE 



99 



ConliunrJ from page 96] 

 sliapc of tlie licail arc the same varieties that exliibit thcin- 

 soItcs in the whole external form of man. Now, if the.<^e 

 iliffcrences of bodily structure arc marks of diversity of 

 nature, the inequalities of the skiiU (which cannot be exempt 

 from the process) will also indicate the same, or to come 

 to the point, will indicate diversity of brain conformation, which 

 is just 'the doctrine of plirenologj-. Assuming it to be established, 

 then, that the " cause that determines the shape of the head " is 

 l>ecnliar conformation of brain, the pertinent remark of Professor 

 Lawrence forms a fitting supplement : — " If the mental processes 

 be not the function of the brain, what is its office ? In animals, 

 which possess only a small part of the human cerebral structure, 

 sensation exists, and in many cases more acute than in man. What 

 <'niployment shall we find for all that man possesses over and above 

 I liis portion — for the large and prodigiously developed human hemis- 

 pheres ? Are we to believe that these serve only to round off the 

 ligureof the orgjin, or to fill the cranium ? " 



With regard to the opinion of Mr. G. H. Lewes, that the brain acts 

 as a whole, and that its functions are not localised, one merely 

 requires to point to Dr. Ferrier's researches in cerebral physiology, 

 by which it has been proved that the individual convolutions ore 

 ^t*parate and distinct organs. A. B. 



POPULAR ELECTRICITY. 



[73] — I write to suggest that now that electricity is becoming of 

 such vast importance in the world, it is very desirable that a sound 

 elementary knowledge of its principles should be widely dissemi- 

 nated, and that Knowledge might be an available medium for con- 

 tributing to this result. Would it not be a good thing that a scries 

 of papers on this subject (including magnetism) should be pub- 

 lished in Knowledge ? The papers should be simple, and should 

 suggest experiments which any person of intelligence might try for 

 himself without elaborate or expensive apparatus. Sometliing in 

 the style of Tyndall's "Lessons on Electricity," but extending, of 

 course, to current electricity. I venture to think that such a series, 

 if produced bj' a competent hand, would be extremely popular with 

 young people, whose desire for information in this direction is very 

 great. — Yours, &c., Daniel Jones. 



COMETS' TAILS. 



[74] — I have read with great interest your excellent paper on 

 Comets, but am sorrj' to find no other theorj- can be introduced to 

 account for the tails always pointing away from the sun, exce))t 

 that of solar repulsion. Such a theory, I am sure, should not be 

 adopted without the most conclusive and perfect evidence of its 

 existence ; because, if we introduce a resisting medium into the 

 solar and stellar system, we see in it the germs of its own destruc- 

 tion, which, although for a time making no effect upon the move- 

 ments of the ])onderous planets, must, in the end, make itself felt, 

 oven though that medium be of the rarest tenuity. I once heard a 

 theory propounded, that comets were simply lenses, and the sun 

 shining through them produced the appearance of a tail ; that 

 might apply to telescopic comets, without any indication of a 

 imcleus, but not otherwise, for Sir John Herschell tells us the 

 nucleus of a comet is opaque. The theory is, as far as I know, a 

 novel one, and the readers of Knowledge must jndge for themselves 

 of its value. — Yours, Ac, J. D. 



THE SUNS DISTANCE. 



[75]. — The latest determination of the velocity of light, by 

 Michelson, gives 186,305 miles per sec. in vacuo. Supposing that 

 the time interval for the passage of light across the major axis of 

 the earth's orbit, which is given as 9866 sees., may be relied on to 

 tbe f*^ part of a second, as is likely, considering the numerous and 

 accurate observations on Jupiter's satellites ; may not the deduced 

 semi-axis of the earth's orbit, which, is 91,904,256 miles, be trusted 

 as far as the first four figures '' The corresponding parallax wonld 

 be 8"'895, round which all the best determinations seem to centre, 

 such as 8"88 from transit of 1874, 8"'91 by Hanen's lunar method, 

 8"894, and 8"'855 from observations on Mars. It appears that 

 Michelson's method, which is based on an extension of Foucault's, 

 gives a result which may be relied on almost down to the unit's 

 place : for the interval to be measured was the passage of light over 

 a distance of about 4,000 yards, and the direct deviation obtained 

 was about 150 times that obtained by Foucault. — Yours, &c. 



Marlborough College, Nov. 19, 1881. , H. L. Callendab. 



[Considering the somewhat wide discrepancies between the 

 observed time of appearance and disappearance of Jupiter's satel- 

 lites, according to the telescope employed and the observer's eye- 



sight, we should be disposed to doubt whether the method referred 

 to can be trusted as likely to give results to the degree of accuracj* 

 you mention. Aberi-ation is regarded as more trustworthy. — Ed.] 



THE METRICAL SYSTEM. 

 [76] — Sir W. Thompson, in his address at Y'ork, referring to the 

 metrical system, says, "to it we are irresistibly drawn in all 

 scientific and practical measurements, notwithstanding a dense 

 barrier of insular prejudice most detrimental to the islander." 



It would be superHuous to enlarge here upon the many advan- 

 tages of the metrical system of weights and measures which are tet 

 forth and explained in so many elementary treatises ; but if you 

 oould find space in your columns for two or three examples, illus- 

 trating the saving of labour that their adoption would introduce 

 into the computations of every-day life, I cannot but think that you 

 would make converts, and by facilitating calculation, promote 

 accnracy, the stepping-stone to all knowledge. 



Take an ordinary example from agriculture ; — 

 A field of 6 hectares, 41 ares, CG square metres, so\vn with wheat, 

 at 250 litres to the hectare, would require 

 6-41G6 X 250 = 1,543-8500 litres, 



= 15 hectolitres, 44 litres of seed. 

 If the wheat is of specific gravity 0'80, the whole quantity would 

 weigh 1544 x 60 = 12352 kilogi-ammes. 



Again, the seed required would be 



2*5 litres for every are, 

 or 0'25 litres for every square metre. 

 Let the same field be ploughed up to the depth of 2 decimetres 

 (nearly eight inches) , and suppose that the specific gravity of the 

 soil is 2, every square metre of the soil ploughed up will weigh 

 2 X 2 y 100 = 400 kilogrammes, and the whole soil of the field 

 ploughed to the depth of 2 decimetres will weigh 



64,166 X 400 = 25666100 kilogrammes, 

 = 256664 metrical tons. 

 It then becomes very easy to compute the proportion of any 

 manure to the available soil. 



Let the amount of manure applied be 1,000 kilogrammes per 

 hectare : — 



1000 kilogi-ammes per hectare 

 = 10 kilogrammes per are 

 = 100 gi-ammes per square metre 

 = 1 gram per square decimetre, or 2 cubic decimetres of soil, 



=i= 00025. 



If tlie amount be 600 kilogrammes per hectare 

 = 6 kilogrammes per are 

 = 60 grammes per square metre 

 = *6 gram per square decimetre 



-i^=00015- 



When great accuracy is required, the u£c of logarithms will, of 

 course, much facilitate the calculation, but they may be disiJcnsed 

 with for ordinary practical purposes. Now, let anyone trj- to work 

 out such simple problems with a field of the same size expressed in 

 English measures, viz., 15 acres, 3 roods, 17 poles, and the seed 

 sown at 3 bushels per acre. He will see what an amount of labour 

 they involve. Indeed, at the outstart, we are met with such an 

 anomaly as this, that while the yard is our standard measure of 

 length, few persons could give the length of the side of a square 

 statute acre, such side being 69 yards and a long fraction (695701). 

 Nor is the matter much facilitated when we find that 30] square 

 yards go to one pole. 



Should you think these remarks not too technical, I shall recur 

 to the subject with some other examples in a future number, and 

 beg to subscribe myself, yoiu:s, Ac, 



MlCBOCBITH. 



[We thank ," Microcrith " for his excellent illustration of the 

 value of the metrical system. It is actually easier in dealing with 

 the second form of the above problem to convert the English 

 measures into the metrical system, then to work the problems 

 as " Microcrith " has done, and to turn the answers into English 

 measures, than it is to work them tlu'oughout with the English 

 measures. — E d.] 



CAUSE OF GRAVITY. 

 [77] — In your note to letter No. 31 (page 59) on this subject, it 

 is stated as a " demonstrated fact that the action of gravity is 

 communicated far more rapidly than light travels." I beg to ask 

 an explanation of this, as I was not aware that the action of gravity 

 was "communicated" at all in the sense of "travelling" (or of 

 crossing over a space during a greater or less lapse of time). An 

 far as my present knowledge goes, the statement reminds me (I give 



