Dec. 9, 1S81.] 



• KNOV/LEDGE 



121 



CinlinMd from page 118] 



BRAIX AND BRAIX CASE. 



' 114] — In Letter 42, page 78, of Knowleuge, Charles Hamilton 



k< tliree pertinent questions. Leaving you to answer the first two 



you best cm, allow me to make a few brief remarks on the 



; .-(, viz., " Does the brain shape or mould the form of the cranium 



..r skull '^ " Dr. La^rrence, late Professor of Anatomy and Surgery 



ii> the College of St. Bartholomew's Hospital, London, in his 



l.i-cturea on Man," says of the skull that " the general capacity 



I particular forms depend entirely on the size and partial de- 



.pment of the brain." While Dr. Mayo, late Trofessor of 



A .atomy and Surgery to Royal College of Surgeons, in his work on 



■ Human Physiologv-," after considering the relation between mind 



:iihI brain, says, "Then it is certain that the skull is formed after 



ill'' brain, and moulded upon it ; and that very moderate attention 



1 enable an anatomist, for the most part, to distinguish those 



Miinences which arc caused by inequalities of bone from those 



;ili mark the proportions of brain." Dr. Turner, Professor of 



^ "itomy in the University of Edinburgh, in a paper read before the 



i; yal Society of that city, on Jan. 19, 1874, says, " The outer sur- 



I;"'' of the skull does not correspond in shape to the outside of the 



bniin." 



Now, sir, what is the meaning of all this ? Out of mere curiosity 

 1 liave consulted medical men with regard to the mutual relations 

 v'f skull and brain, till I am tired, and, although they set out with 

 I !['■ observation that the question is simply one of fact, no two of 

 thrni give rae the .same answer. Indeed, they are completely at 

 !\'S and sevens. What I wish to point out as the moral of all this 

 1- I liat for us there is nothing left but to fall back upon nature, 

 "liich, as Dr. Gall said, is the only infallible testimony, and bring 

 till' inquiry to the test of observation and of fact, leaving medical 

 mi'M to dogmatise as they choose. 



Glasgow, Xof. 25, 1881. A. B. 



TECHNICAL TERMS— SCIEXTIFIC NEWS— ILLUSION. 

 115] — I take the liberty of sugggesting that you request ojrre 

 -i'"iidents to place the technical terms they employ side by side 

 ■• iMi the popular modes of expression, for the reason given in letter 

 p. 78. In letter 46, p. 79, in the fourth line of the second para- 

 ph, Mr. Allen, in alluding to the shape of the forehead, uses the 

 ■'1 " orthom^topy," bracketing the meaning. So far so good, but 

 i'lily in the next line he makes use of the term " prognathism " ; 

 three lines further appears " orthognathism," and again five lines 

 below the word " Sella." Writers must know that only speciali.sts, 

 or classical scholars, would understand the meaning of terms such 

 .'13 these. What, therefore, I take the liberty of suggesting would 

 be your placing a standing notice to correspondents at the com- 

 mencement of the correspondents' column. Also that, under the 

 head of " Scientific News," you give weekly, or from time to time, 

 t!i'' most recent inventions or discoveries in physical and mechanical 

 ^' i 'nee that would be of popular interest. 



F. H. S. 

 In reference to the drawing I sent you last week illustrating an 

 o| tical illusion (letter 65, p. 95), the effect is much more striking 

 with the horizontal line uppermost. 



I It seems to us more striking still when the angle is put upper- 

 most or lowest. — Ed.] 



THE DURATION OF A FLASH OF LIGHTNING. 



! 116] — Can you or any of your readers give me information on 

 1 1ll' following two points ; — 



1. Did Wheatstonc or anyone else ever make an experiment on a 

 ll:isli of lightning to determine the time of its duration ? 



2. If so, what was the nature of the experiment, and where is it 

 do.'icribed ? 



I may state, to prevent misapprehension, that I am quite aware 



tliat Wheatstone made experiments to determine the duration of an 



' trie spark produced under certain definite conditions, and that 



^'' experiments are fully described in the '' Transactions of the 



il Society." But I find it explicitly stated by several ivriters of 



iiiwii authority — for example, Mascart,* Daguin,t Ganot,J — that 



Wheatstone made experiments on the lightning flash itself. They 



say he employed a white disc with black ray.s, ver^- close together, 



whichhe put in rapid rotation, and so placed that it was illuminated 



1 V each succeeding flash of lightning. The details of the experiment 



U'- fully given by Dcschamel,§ who, however, does not ascribe it to 



'Electricife Statique, ii., 561. iTraiU de Phiisique, iii., 213. 



t " Treatise on Physics," translated by Atkinson. Sixth 

 Edition, p. 828. 



§" Natural Philosophv," translated bv Everett. Sixth Edition. 

 p. 641. 



Wheatstone. Now I have searched in vain for the authentic 

 record of this experiment, and 1 should feel greatly obliged to 

 anyone who can give me information about it in the pages of 

 Knowledge. 



I think you will agree with me that the subject is not without 

 interest for your readers, when I mention the widely different state- 

 ments that have been put before the public, quite recently, regard- 

 ing the duration of a flash of lightning. According to Mascart,* 



it is less than of a second ; according to Deschanel, + it is less 



1,000 ^ 



1 _ , ,. . ™ , „. , ,, 1 



than the - 



and according to Tyndall,* less than 



10,OL'0 " ' - '" ■" 100,000- 



" Wheatstone has shown that it certainly lasts less than a millionth 

 part of a second. "§ Of course, if this last statement be true all the 

 others are, in a certain sense, true also ; but they do not give us 

 the whole truth. — Yonrs, &c. Geh.ild Molioy. 



Catholic Universitv of Ireland, 86, Steplien's-green, Dublin, 

 Dec. 2, 1881. 



LUMINOUS PHENOMENON. 



[117] — I find in the volume of the Leisure Hour for 1853, under 

 the title of "Astral Wonders," a pamphlet on a lecture delivered by 

 the Rev. J. Craig, M.A., a short time before. 



I wish to call your attention to the following. He says : — '' When 

 I was a boy, from some cause'or other I was put into a dark room and 

 tried to escape out of it. I had a knife in my pocket, and I began 

 to cut a hole in tte door to try to get quietly away by coming at the 

 latch. Still, something occurred which induced me to remain where 

 I was. I heard a footstep, and I knew I was not doing quite right. 

 When I pulled my hand back the sun happened to be shining very 

 much and I saw little globules running off in all directions. I 

 thought even then this was very remarkable. I again put out my 

 hand, and on pulling it back I saw the little globules running off as 

 before, When I grew up to be a man I began to think of that childish 

 thing. I felt certain then that light was a fluid and could run off 

 our fingers like water ; and if you feel any interest in light and will 

 examine for yourselves you will see that light is truly a fluid ; it has 

 its waves, its currents, its ocean deeps, and our telescopes may yet 

 tell us something of its tidal surroundings." 



I shall be most happy to receive any information on the above sub- 

 ject, viz. (that of light being a fluid) which you or any of your corre- 

 spondents may afford me. — Yours faithfully, W. M. M. 



[Mr. Craig seems to have mistaken a physiological for a physical 

 phenomenon. His experience showed, as many others do, that 

 '' seeing is not always believing." In a railway accident I have seen 

 " astral wonders," as I have when I have been pitched on to my 

 head by a galloping horse, but I do not infer that stars reside in my 

 head. — Ed.] 



A £5 TELESCOPE. 



[118]— "Twenty " (letter 48, p. 79) cannot obtain an absolutely 

 perfect instrument for £5, but for this sum he can obtain from 

 numerous opticians a telescope which has all that is necessary for a 

 beginner, and the other apparatus he can get from time to time (and 

 at no considerable cost), as he becomes more experienced. The £5 

 telescopes advertised are refractors ; that is, the usual sort with a 

 lens (object glass, of 3 in. diameter) at the end of a tube. The 

 other sort, termed reflectors, having a silvered mirror at the bottom 

 of a tube reflecting the image to a focus at the top, are less costly 

 (if a large instrument is wanted), but require verj- nice manage- 

 ment, and should only be purchased after considerable experience 

 is acquired. The £5 glasses are very good ones indeed, containing 

 all the groundwork of a first-class instrument, and will be found all 

 that " Twent}' " wants to commence with. After a time, he will 

 like a tall wooden tripod-stand (which can be made by a handy 

 man), and will want to add a " finder ; " that is, a miniature tele- 

 scope fixed at the side, by looking through which a celestial object 

 can be immediately brought into the field of view of the larger one. 

 He will also want a couple of extra eyepieces of different powers to 

 the one supplied with the instrument, as different objects require 

 different powers to show them at their best. After this (if his taste for 

 observation developes), he may like to replace the object glass with 

 one by a celebrated maker. These things, however, only result from an 

 increased passion for the study of the heavenly bodies. The instru- 

 ment, as supplied for .£5, contains all that is necessary for a 

 beginner, and one who simply wishes to observe the stars for occa- 

 sional plea.surc will never want anything more. Such accessories 



• Electrici'i! Sfatique, ii., 561. t Traits de Physique, iii., 642. 

 X Fragments of Science, fifth edition, p. 311. 



§ Lecture delivered in the City Hall, Glasgow, published in 

 Nature, Vol. ixii., p. 341. 



