October 3, 1895] 



NATURE 



547 



was so. The remains of primitive architecture in Greece — 

 particularly at Tirj'us — show that wood must have entered 

 largely into architectural constructions ; amongst other evidences, 

 the traces oi wooden door-cases cannot be explained away. 

 Perrot and Chipicz, with whatever amount of fancifulness there 

 may be (and there is no doubt much which is altogether hypo- 

 thetical) in their restorations, do come legitimately to an ex- 

 planation of the Doric gutta; both under the triglyphs and 

 beneath the niutules, as typical of the ends of wooden pegs or 

 trenails in timber construction, which is sufficient for the argu- 

 ment in the review, in which there was no intention to approve 

 Perrot and Chipiez' restorations and deductions any further than 

 that. 



(2) As to the second objection taken to the review — the re- 

 mark respecting the cupola of St. Paul's. The remark in the 

 review had reference to the objection that the external outline 

 of the dome was distinct from the internal, and not to the 

 question of support of the lantern ; but with reference to the 

 latter point, when the lantern of St. Peter's is quoted as sup- 

 ported by a more legitimate construction than that of St. Paul's, 

 it may be asked : Why the construction of St. Peter's dome, 

 which is absolutely dependent for its safety on the iron chains 

 by which it is hooped together, is preferable to that of St. Paul's, 

 where the lantern has a much securer, and therefore not less 

 legitimate, support in Sir Christopher Wren's cone ? 



(3) One remark only on the objection raised to the style of 

 Milan Cathedral. The detail is said to be wretched. That it 

 does not conform to the canon of Northern Gothic can be 

 readily conceded, but that the shafts of the magnificent forest of 

 pillars which support the interior are wretchedly designed, and 

 unsuitable to the intended effect, is not so easy to admit. 



The Reviewer. 



Do the Components of Compound Colours in Nature 

 follow a Law of Multiple Proportions ? 



This question, put by Mr. W Howard Collins .in Xati^re 

 (p. 438), may be answered in the negative. 



In practical work there is no indication of such a law. It is 

 found that the two rays, which together produce a compound 

 natural colour, may be in any [iroportions ; when there is a mul- 

 tiple proixjrtion, and in some cases there must be, it is only as 

 forming part of a series of variations, such as are frequently found 

 within the limits of a single popular colour term. How wide 

 these proportions may be, can be illustrated by comparing them 

 to the varying proportions of two irregular curves towards each 

 other. 



The examples of foliage quoted can only be taken as repre- 

 senting individual instances. Variations of climate, age. cultiva- 

 tion, and aspect alter the colour proportions of a given variety 

 of leaf ; indeed, such variations are sometimes found in the same 

 leaf. JosEi'ii W. LoviBOND. 



Salisbury, September 23. 



In view of the letters, recently printed in Nature, by Mr. 

 H. H. Pillsbury and Mr. Herbert Spencer, it may be well to 

 state that Chevreul published an " Expose dun moyen de definir 

 et de nommer les couleur d'apres une methode precise et 

 experimentale " (Paris, 1861, also Mem. dc T Acad, xxxiii.), in 

 which elaborate charts are given showing the colours defined by 

 a decimal system and in ten degrees of saturation. 



Recently Prof W. llallock, of this College, has painted discs 

 with standard colours, and detennined their wave-lengths with 

 the spectroscope. These discs were then used to study 6000 

 samples of coloured objects, and formuke were determined for 

 some 500 named colours. These formula; have been used for 

 defining the names of colours in the new " Standard Dictionary " 

 (l'"unk and Wagnall's, New York). 



J. McKeen Cattei.i.. 



Columbia College, New ^'ork, September 20. 



A Problem in Thermodynamics. 



It may interest some of your readers to know that the 

 problem in thermodynamics, propounded by Mr. Blass in your 

 number of .\ugust 29, has actually been put to the test. I 

 pointed out Mr. Blass's letter to my brother, who is a freezing 

 engineer, and he showed me a co])y of the Zcitschrift fiir die 

 Cesamiiielte Kdlte-Iiidiislric (Nfunich) for August, in which an 



NO. 1353, VOL. 52] 



account is given of a machine on exactly the principle )lr, 

 Blass suggests, by which llerr Linde has succeeded in liquefy- 

 ing air. It would appear, therefore, that the "theoretical 

 minimum of temperature produced at c " would be determined 

 by the point of liquefaction of the gas employed ; with a perfect 

 unliquefiable gas it would, I suppose, theoretically, be absolute 

 zero. Edward T. Di.'cox. 



Cambridge, September 22. 



THE NEW MINERAL GASES. 



OUR knowledge of the spectra and other conditionings 

 of the new mineral gases has received an im- 

 portant addition in the communication from Drs. Runge 

 and Paschen which appeared in last week's N.\TURE. The 

 employment of exposures extending over seven hours 

 has given a considerable extension in the number of 

 lines, and the bolometer has been called in to investigate 

 lines in the infra-red ; better still, they have employed 

 well-practised hands in searching for series of lines. 

 Operating, by chemical means, upon a crjstal of cl^veite 

 free from any other mineral, they have obtained a pro- 

 duct so pure that from these series there are no out- 

 standing lines. \'ery great weight, therefore, must be 

 attached to their conclusions, and there are several 

 points of contact with the work upon which I ha\e been 

 engaged from a slightly different stand-point since last 

 .\pril, when Prof. Ramsay inade his fortunate discovery 

 of a terrestrial source of helium. 



I will touch upon some of these points seriativi. 



In the first place, there has never been the slightest 

 doubt in my mind that it was a question of gases and not 

 of a gas. The spectroscopic evidence in the laboratory 

 alone was complete, and the case was greatly strengthened 

 when the behaviour of the various lines in the sun and 

 stars was also brought into evidence. Drs. Runge and 

 Paschen also declare that the gas given off even by 

 a pure ciystal of cl&veite is not simple, but consists of 

 two constituents. To the one containing the line D3, 

 which I discovered in 1868, the name helium remains ; 

 the other for the present, we may call "gas X." The 

 chief lines of these two constituents are as follows, accord- 

 ing to Runge and Paschen : 



Helium. 

 5S76 

 4713 

 4472 

 4026 

 3889 



Gas X. 

 667S 

 5048 

 5016 

 4922 



Last May 1 wrote as follows' : — 



"The preliminary reconnaissance suggests that the gas 

 obtained from broggerite, by my method, is one of com- 

 plex origin. 



" I now proceed to show that the same conclusion holds 

 good for the gases obtained by Profs. Ramsay and Cl^ve 

 from cleveite. 



" For this purpose, as the final measures of the lines of 

 the gas as obtained from cleveite by Profs. Ramsay and 

 Clfeve have not yet been published, 1 take those given by 

 Crookes, and Clt;ve, as observed by Thalen. 



" The most definite and striking result so far obtained is 

 that in the spectra of the minerals giving the yellow line 

 I have so far examined, I have never once seen the lines 

 recorded by Crookes and Thalen in the blue. This 

 demonstrates that the gas obtained from certain speci- 

 mens of cldveite by chemical methods is vastly different 

 from that obtained by my method from certain specimens 

 of broggerite, and since from the point of view of the 

 bltic lines, the spectrum of the gas obtained from cliveite 

 is more complex than that of broggerite, the gas itself 

 cannot be more simple. 



" Even the blue lines themselves, instead of appearing 



1 Froc. Roy. Soc., vol. Iviii. p. 114. 



