4i6 



NA TURE 



[March 6, 1902 



theory as well as on experiment, we are forced to conclude that 

 the diameter of a molecule cannot be larger than 0'003^. On 

 the other hand, the specific gravity of a molecule of air, for 

 instance, appears to be very great, viz. five times that of water (see 

 Meyer, " Die kinetische Theorie der Case "). This maNimum 

 value of the diameter of a molecule is so enormously smaller than 

 the values demanded by Prof. Arrhenius' theory that the latter 

 appears to be incompatible with any assumption which regards 

 the cometary matter as being of a gaseous constituency. In 

 order to explain the repulsion of matter in the tails of comets 

 by the pressure of the sunlight, this matter must be assumed to 

 consist of small drops, each of a bulk sufficiently large to har- 

 bour at least one million molecules within its bounding surface. 

 Whether such an assumption can be justified appears to me 

 very doubtful. At any rate, I'rof. Schwarzschild's profound 

 mathematical investigation makes it absolutely clear that the 

 idea of minute electrically-charged corpuscles — of about one- 

 thousandth the size of a hydrogen atom (see Obserz'alory, 

 February 1902, p. loj)— being propelled by the sun's light 

 towards the earth and causing the various phenomena of aurorre, 

 Gegenschein, &c., receives no support from the mathematical 

 point of view. But, even apart from these difficulties, it can 

 hardly be said that the ingenious theory of Arrhenius settles the 

 question as to the nature of the force acting on the cometary 

 matter. So far it offers no explanation of the remarkable 

 phenomenon of the contraction of the coma with the approach 

 towards the sun. Doubtless this tonlractile force is also of solar 

 origin. But can it be identified with the force which repels the 

 cometary matter in the direction of the radius vector ? It ap- 

 pears to me that the theory in its present form only removes one 

 difficulty by introducing several others. J. IIalm. 



Royal Observatory, Edinburgh, February, 20. 



Experimental Geometry in Secondary Schools. 



I.N the report, in your issue of February 27 (p. 404), of a meet- 

 ing of the Mathematical Association, it is stated to have been 

 the opinion of most speakers that the study of demonstrative 

 geometry should be preceded by a course of work with ruler, 

 compasses and protractor, in which simple measurements and 

 constructions form the chief part. The note continues with the 

 statement that such a course has been adopted in Scottish 

 schools, and in English elementary schools and kindergartens. 



May I venture to point out that there are a considerable 

 number of secondary schools where this kind of work forms a 

 regular part of the curriculum in the lower mathematical classes 

 (this has, for instance, been the cise here for the past three 

 years), and that it has been recognised as a valuable medium by 

 which a boy's interest may be aroused in geometry before he is 

 introduced to the very irksome and difti;ult task of assimilating 

 Euclid's phraseology? C. A. RuMSEV. 



Dulwich College, March 5. 



The Zodiacal Light. 

 The zodiacal light was visible here last night at 7h. 30m. 

 p.m. The base at the horizon was about 16" wide ; the axis of 

 the cone pointed towards the Pleiades, but the apex did not 

 reach much beyond a Arietis. At 7h. 45m. it was brightest ; at 

 8h. it had faded out, possibly on account of mist in the air, as 

 a fog set in about an hour afterwards. J. P. Maci.kar. 



Chiddingfold, Surrey, March 4. 



Contributions to Anatomical Journals. 



Prof. Hu.ntington, of Columbia University, has called my 

 attention to a paragraph in an article on " A New Journal of 

 Anatomy " in your issue of January 9 to which he, naturally, 

 takes exception. 



In justice to Prof. Huntington, I beg leave to state that he 

 had no p.irt whatever in the recommendation, acceptance or 

 production of either of the papers on which your critic anim- 

 adverts. 



The first of these was accepted by one of my British co- editors 

 and sent to me for publication, the author supplying the plates. 

 For the second I, solely, am responsible. 



The method of the higher criticism is not always trustworthy 

 when its results can be checked by contemporary history. 



Ai.EX. MALAI.I>rER. 



New Museums, Cambridge, February 14. 



NO. 1688. VOL. 65] 



I REiiRET (0 say that my statement concerning Prof. 

 Huntington and the origin of the paper which I described was 

 based on hearsay, and in face of Prof. Mjcalister's letter I can 

 but tender Prof. Huntington my sincere apologies. 



I am relieved to find that the author provided the pi 



February 26 



The Writer 01 ihe Review. 



FURTHER DEVELOPMENTS IN WIRELESS 

 TELEGRAPHY. 



CINCE the article which appeared in Natiire last 

 •-^ week 'was written, some further details concerning 

 Mr. Marconi's Transatlantic signalling have been pub- 

 lished, and also another success attained by the inventor 

 has been announced. The information with reference to 

 the latter point is contained in a telegram from the New 

 York correspondent of the Daily Telegraph, which ap- 

 peared in that paper on Monday last. Messages, it 

 seems, were transmitted from Poldhu to the Philadelphia, 

 whilst that ship, on board of which was Mr. Marconi, 

 was on her way from this country to New York. Five 

 messages in all were received, the first when the 

 Philadelphia was at a distance of 250 miles from the 

 Lizard, and the last on February 25, when the distance 

 had been increased to 1551 miles. In addition, a signal 

 of the much-talked-of letter '■ S " was received at a dis- 

 tance of 2099 miles. The news is confirmed by the 

 following telegram from Mr. Marconi, which is contained 

 in a letter from the Wireless Telegraph Co. to 

 Wednesday's Times : — 



" Health good. Received messages 1551 miles. Test letter 

 at 2099. All on tape receiver. Records duly attested by ship's 

 officers. — Makconi." 



The chief interest of these results lies in the fact that 

 the received messages, including the signal " S," were 

 recorded on the tape of the receiving apparatus, and not 

 merely heard in the telephone, as was the case with the 

 Transatlantic signal. Mr. Marconi must feel greatly 

 gratified at thus having visible record of the success of 

 his experiments in this instance, as it removes the possi- 

 bility of the suggestion that he was deceived by the wish 

 to hear being father to the thought that he heard. 

 Messages were naturally only transmitted in the one 

 direction, as the transmitting apparatus on board the 

 Philadelphia was not so powerful as that at the Cornwall 

 station. 



The further details as to the Transatlantic signalling 

 to which we referred above are published in an article 

 on Mr. Marconi in this month's Centuty Magazine. 

 This article, the proofs of which have been read by 

 Mr. Marconi, contains an account of the development 

 of wireless telegraphy, and is illustrated by a number of 

 interesting pictures. We reproduce here a photograph of 

 the transiTiitting station at Poldhu from which all the long- 

 distance signals have been transmitted, which shows very 

 clearly the group of twenty masts, each of which is 2 10 feet 

 high. The power is obtained from an alternate-current 

 generator of jS horse-power. There is thus more than two 

 hundred times as much power used as in the signalling 

 apparatus installed on board ships using the Marconi 

 system. It will be noticed that in the later work de- 

 velopment has taken place rather along the Imes of 

 increasing the output of power than of using higher 

 masts. Mr. Marconi, it is said, considers that a mast about 

 200 feet high is the most suitable from all points of view, 

 and in some remarks, which we quote at the end of this 

 article, states that he thinks that any desiied distance 

 could be bridged given sufficient power. 



A good deal of objection is still raised on the question 

 of syntony, and it is pointed out that although tuning 

 has been obtained with sufficient accuracy to prevent 

 interference, this does not prevent the picking up of 

 messages by an outsider who should experiment with a 



