April 5, 1906] 



NA TURE 



535 



Formula for finding the Date of Easter. 



1 1 may be of interest to some of your readers to know 

 of the following empirical formula — attributed to the 

 famous mathematician Gauss -for determining in an easy 

 manner the date on which Easter falls in any year from 

 1900 to 2100 : — 



if ihe year 



(il The number of ihe year is divided by 19; re- 

 mainder=a. 



(2) The number of the year is divided by 4 ; re- 

 mainder^. 



(3) The number of the year is divided by 7; re- 

 mainder =c. 



(41 19x0 + 24 is divided by 30; remainder = </. 

 (5) 2 X b + 4C + 6x(i+5 is divided by 7; remainder = e. 

 Easter will be the 22 + d+e of March, or, if this number 

 exceed 31, it will be the d+e — 9 of April. 



The calculation for the present year is as follows : — 



I the insolubility of butter fat in alcohol. Butter fat is, 

 however, soluble in alcohol, and I have no doubt whatever 

 that a process of fractional precipitation from this solution 

 would enable us to ascertain with fair accuracy what the 

 real constituents are. My own experiments certainly 

 pointed to a great number of separate glycerides being 

 present, palmitin and stearin separating out in tolerable 

 purity. The separation of the lower fatty acid compounds 

 is more difficult to attain, probably owing to their exist- 

 ence as esters. It would be interesting to know whether 

 the theory of the presence of triglyceride rests upon a more 

 stable foundation than that of Bell's statement. 



J. II. Lester. 

 Royal Exchange. Manchester, March 17. 



1906 



4 + 18 



(s) (2x 2 ) + (4 x2)4-(6xi8) + 5_ l7| 6 



(a=6) 

 (i=2) 



U = 2) 



(rf=iS) 

 («' = 6) 



As 22 + 18+6 is in excess of 31, we take the alternative 

 18+6 — 9=15, on which day of April Easter falls this 

 year. Chas. Leigh. 



The Victoria University of Manchester, March 30. 



Chinese Names of Colours. 



In your issue of January 11 (p. 246) Mr. Alfred H. Crook 

 writes respecting the name given by the Chinese to a 

 certain tint of blue, which he translates quaintly as " snow- 

 green colour." The following explanation may be of 

 interest to him and to others of your readers. 



W Hsiieh, the word he translates "snow," also means 



ice," and to the natives of southern China is far better 



known in reference to the latter object than to the former, 



as the same name is applied to both natural and artificial 



ice. 



B Tsing originally meant "clear," "tranquil," 

 " smooth " (applied to water). The change from " smooth 

 water " to the " colour of smooth water " is an easy one, 

 so that a secondary meaning of the word is " sea-green " 

 or " sea-blue." Quite different words are used to express 

 other green tints, such as grass-green, and other blue 

 tints, such as indigo-blue. 



Putting the two words together, one finds the meaning of 



& pf 8 (hsiieh tsing seh) to be " ice-blue colour " or 

 "blue ice colour." Anybody who has noticed the tint of 

 ice in great masses such as one gets in north China and 

 in Switzerland, and who has seen the colour referred to by 

 Mr. Crook, will agree with me in saying that the name 

 given by the Chinese, far from being fanciful, is very 

 appropriate. L. 



Hong Kong, February 15. 



The Adulteration of Butter. 



My attention has been directed to an article in your 

 issue of March 15 on " The Adulteration of Butter " in 

 which your contributor refers to the composition of butter 

 fat as a triglyceride of oleic, palmitic, and butyric acids, 

 or as containing such a substance. Some years ago I 

 traced this opinion to Mr. Bell, a former analyst of Somer- 

 set House, who appears to have based his conclusions upon 



NO. I9OI, VOL. 73] 



Your correspondent scarcely does justice to Dr. Bell's 

 observation. 



Whether butter fat is completely soluble in alcohol or 

 not depends upon the volume, strength, and temperature 

 of the solvent. Bell showed that when the simple glyceride 

 tributyrin was mixed with melted ordinary fat to the 

 extent of 10 per cent., it could be entirely removed by 

 treatment with warm alcohol. But when butter fat was 

 similarly extracted, from 2 per cent, to 3 per cent, only of 

 the fat was dissolved out, and the soluble portion was not 

 tributyrin. Therefore the butyric acid of butter fat is not 

 present as the simple glyceride tributyrin, but chiefly or 

 wholly as a mixed glyceride. Further, the portion dis- 

 solved from the butter was found to contain " soluble " 

 and " insoluble " acids in proportions agreeing closely with 

 those required for the mixed glyceride oleo-palmito- 

 butyrin. 



Some years later (Proc. Chem. Soc, 1889) Blyth and 

 Robertson noted the isolation from butter fat of a crystal- 

 line mixed glyceride, to which they ascribed the formula of 

 palmito-stearo-butyrin. 



The " presence of triglyceride " in butter fat will hardly 

 be questioned ; what your correspondent has in mind is, 

 apparently, the occurrence of mixed (i.e. complex) 

 glycerides. Many such have been isolated from various 

 natural fats in the last few years ; this is, in fact, the most 

 notable feature in the recent chemistry of fats. That 

 complex glycerides exist in butter Bell's and Blyth's experi- 

 ments leave no reason to doubt, though more rigorous proof 

 of their precise composition is desirable. 



March 20. C. SlMMONDS. 



The Existence of Absolute Motion. 



In discussing this question it is surely necessary to place 

 stress on the contrast between the places of absolute direc- 

 tion and absolute position in dynamics. The result of 

 observation is that the laws of motion are competent to 

 explain such phenomena as nutation and retain the simple 

 Newtonian form when certain directions which can be 

 found with reasonable accuracy are assumed to be absolute. 

 The contrary assumption, that these directions were not 

 absolute, but moving with absolute angular velocities, say 

 of the order of one degree per second, would necessitate a 

 re-statement of the laws of motion involving great loss 

 of simplicity- In the same way, we cannot without loss 

 of simplicity suppose that the acceleration of the earth 

 with respect to the centre of the solar system differs greatly 

 from the absolute acceleration, and suggest that the 

 material universe has an absolute acceleration of the order 

 of one hundred miles per second per second. 



On the other hand, the laws of motion would not be 

 modified in the slightest if the whole universe possessed a 

 uniform and constant absolute velocity, however great that 

 velocity might be, even, for example, ten times the velocity 

 of light. Compared with such a velocity as this, the 

 veloi it) of the solar system relative to the centroid of the 

 visible stars is probably insignificant. Evidence as to the 

 existence of such a velocity must be sought elsewhere; 

 dynamics alone will not supple it. 



F. J. YV. Whipple. 



Merchant Taylors' School, E.C. 



