540 



NATURE 



[February 23, 191 1 



fulness is the single-plate or screen-plate process. 

 Here evideniiy the author writes with considerable 

 experience and even enthusiasm, and as those parts 

 that deal with the "autochrome," "dioptichrome," 

 "Thames," and "omnicolore" plates have been re- 

 vised by the respective makers of these plates, there 

 is excellent guarantee that the details given are 

 trustworthy. 



There is always a difficulty when entering into par- 

 ticulars on such a subject, that commercial products 

 are liable to vary, and it is often impossible for one 

 person to krK)w the extent of this variation in every 

 section of the subject. Just one example will indicate 

 the need for bearing this in mind. Dr. Johnson says 

 of the " dioptichrome " plate that the '■ first black 

 condition is very perfectly fulfilled." That means 

 that the red, green, and blue patches on the colour 

 screen are so proportioned that the general colour 

 presented to the eye is a pure grey. We have just 

 examined two screens of this make, and one is a 

 rather fine green and the other pinkish. The pre- 

 liminary chapters on the eye, colour vision, and colour 

 blindness, although short, are of much interest. 



Tables for Calculation of Rock-Analyses. By Alfred 

 Harker, F.R.S. (Cambridge: University Press, 

 1910.) Price li-. 



Chemical analyses of rocks are constantly becoming 

 more refined and complete, and, in consequence, if 

 accurately interpreted, are of increasing value to the 

 petrologist. Systems of rock-classification that depend 

 on chemical composition are also now in favour. For 

 these and other reasons it becomes desirable that the 

 percentages of components as stated in a rock-analysis 

 should be translated as easily as possible into per- 

 centages of the constituent rock-forming minerals. 

 Mr. Marker's tables are designed to meet this want, 

 and they have so many valuable features that they 

 should be in the hands of all teachers of petrology. 

 They are very compact, and consequently are cheap 

 compared with the books hitherto in use for this pur- 

 pose ; much time may be saved by their use and long 

 calculations avoided. The method adopted is simple 

 and exceedingly ingenious, and with these tables a 

 student who has not hitherto attempted calculations 

 of this sort may make them more rapidly and even 

 more accurately than by any of the methoids formerly 

 in use. 



Populdre Vortrdge aus dem Gebiele der Etttwickel- 

 ungslehre. By Dr. Wilhelm Breitenbach. Pp. vi + 

 264. (Brackwede i. W. : Verlag von Dr. W. 

 Breitenbach, 1910.) Price 3 marks. 



This little book consists of six popular lectures, deal- 

 ing respectively with the origin of life, recent theories 

 or hereditV', fifty years of Darwinism, Fritz Miiller, 

 the prince of observers, Hermann Miiller. and the 

 historv of the human race. They are written in a 

 clear and interesting style, and, apart from their 

 scientific value, mav be strongly recommended to 

 English students of biology who desire to improve 

 their acquaintance with the German language. 



Open-air Studies in Botany : Sketches of British Wild 



Flowers in their Homes. By R. L. Praeger. Second 



edition, revised. Pp. xiii + 266. (London : Charles 



Griffin and Co., Ltd., 1910.) Price 65. net. 



The first edition of this book was reviewed in Nature 



of June 16, 1898 (vol. Iviii, p. 150). The present issue 



has been revised throughout, but little alteration has 



been made. The nomenclature has been changed 



where necessary to follow that used in the " List of 



British Seed-plants and Ferns," published by the 



British Museum in 1907. 



NO. 2156, VOL. 85] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



A Perpetual Calendar. 



I CANNOT allow the article signed by " W. T. L." in 

 Nature of February 2 to pass without a protest. The pro- 

 posal to make " New Year'.s Day " a dies non, named 

 " New Year's Day," and not a day of the week or of the 

 month, emanated, I believe, from Mr. Alexander Philip, 

 of Brechin. Supposing that January 1 were a Sunday, and 

 supposing that March, June, September, and December 

 were given 31 days, the other months 30 each, February i 

 would always fall on a Tuesday, March i on a Thursday, 

 and so on. This would save much trouble in arranging 

 dates for meetings. But, more important still, the four 

 " quarters " of the year would be equal, instead of, as at 

 present, consisting of 90, 91, 92, and 92 days. Fro.n 

 testimony by railway companies, insurance offices, 

 chambers of commerce, and business men, an alteration 

 which would equalise terms would meet with universal 

 approval. It is difficult to see where the trouble men- 

 tioned by your contributor would come in. It may be 

 stated that authorities in the leading churches have been 

 consulted, and that apparently no objection would b:- 

 raised by them. I am Informed that the Belgian Foreign 

 Office has addressed a diplomatic inquiry at the X'atican, 

 and that the Holy See is not opposed to the reform of 

 the calendar. Surely the organ of English science is. 

 not going to oppose a useful innovation, acceptable to all 

 practical men, which would save an enormous amount of 

 labour in accounting and would simplify all business 

 arrangements. \Villiam Ramsay. 



University College, Gower Street, London, W.C., 

 February 3. 



Alterations in so fundamental a matter as the regula- 

 tion of time and of the calendar must always give trouble, 

 and should not be adopted unless very great advantages 

 would result from the <-hange. Now it appears to the 

 writer that no such advantage would be obtained by 

 making the days of the week always correspond to those 

 of the month ; indeed, in the arrangements of life it is 

 often found convenient that they should not correspond. 

 As to the lengths of the quarters being now unequal, they 

 could be rendered as equal as possible by the simple pro- 

 cess of restoring the original regulation of Julius Caesar, 

 according to which February had 29 days in common years 

 and 30 days in leap-years, and August had only 30 days. 

 \'ery serious inconvenience would probably result from the 

 ignoring of a day every year, particularly as this would 

 have to be extended to two days in leap-vear. 



W. T. L. 



The Progressive Disclosure of the Entire Atmosphere 

 of the Sun. 



Some of the remarkable spectroheliograms which you 

 reproduce in connection with your report of M. Deslandres' 

 lecture, delivered by that gentlemari at the Royal Institu- 

 tion on June 12, 1910, call for special comment. This 

 applies more especially to the pair which represents th-^ 

 sun for March 21, 1910. I had the good fortune to 

 observe spectioscopically an exceptionally fine prominence, 

 which persisted for two entire synodic rotations. During 

 some of the early days in March it graced the west limb, 

 then reappeared in the east about a fortnight later, showed 

 again in the west, reappeared in the east once more 

 towards the middle of April, and gave a final appearance 

 in somewhat modified form on the west limb on April 2S. 

 It is fullv described and illustrated in an interesting note 

 by Dr. F. Slocum in the Astrophysical Journal for 

 September, 1910. 



This prominence, while of fair altitude, was more con- 

 spicuous with regard to its latitudinal extent. But as 

 regards altitude, it should be mentioned here that the 

 Yerkes photographs were taken in calcium light, while 

 my spectroscopic observations were made in hydrogen H=t 

 light, and I have noted on many occasions, before and 



