710 



SCIENCE. 



[N. S. Vol. VIII. No. 203. 



societies, as well as the National Museum, to the 

 very great convenience of everybody concerned. 

 I have never found any difference of opinion 

 among working zoologists on this point. 



Wm. H. Dall. 

 Smithsonian Institution, November 5, 1898. 



THE NERNST LIGHT. 



To THE Editor of Science: Several months 

 have passed since the report of the discovery of 

 a new incandescent electric light by Pro- 

 fessor Nernst, of Gottingen. It was rumored 

 that a Berlin firm had bought the patent for 

 five million Marks, and that we were on the 

 eve of another revolution in the illuminating 

 industry, but till recently very little reliable in- 

 formation has been obtained. In the meantime 

 Professor Nernst has been developing and per- 

 fecting his invention, and his researches have 

 been crowned with such success that we may 

 look forward to the early appearance of the 

 finished lamp, and perhaps the confirmation 

 of the most sensational rumors. 



The astonishing progress in illumination dur- 

 ing recent years has been characterized by a 

 great race between gas and electricity. Scarcely 

 had the incandescent light secured a firm hold 

 in the practical world when Auer von Welsbach 

 made his famous improvement on the gas light, 

 and the possibility of the use of acetylene be- 

 came apparent, so that many believed elec- 

 tricity would after all have to yield the 

 supremacy to gas. Nernst now reclaims the 

 palm for electricity, for he expects that the 

 cost of his light for a whole evening will be no 

 more than that of the Edison for an hour. 



The Nernst light requires neither vacuum nor 

 tender filaments. The essential point of the 

 invention is that when substances like magnesia 

 (magnesium oxide) and clay are heated above 

 3,000 degrees Celsius (6,000° Fahr.— far above 

 the melting point of platinum) a very weak 

 current is suflBcient to keep them in an intensely 

 luminous condition. Either direct or alterna- 

 ting currents may be employed, and the mag- 

 nesia is little injured by use. The only diffi- 

 culty that remains to be surmounted is a prac- 

 tical and inexpensive appliance for heating the 

 substance to the necessary temperature. The 

 work is, however, progressing and those who 



know the ability and courage of the inventor 

 are confident that he will succeed. 



Professor Walter Nernst, though unknown to 

 most people, is a scholar of high rank in the 

 purely scientific world, and his works or their 

 translations are to be found in almost every 

 scientific library. His brilliant researches won 

 him the newly established chair of physical 

 (theoretical) chemistry at G5ttingen, and he 

 is surrounded by advanced students of the most 

 varied nationalities, all of whom greatly ad- 

 mire his fertile mind and genial, inspiring man- 

 ner. His new invention is but another example 

 of the benefit that patient, conscientious scien- 

 tific study is sure to bring to the whole world. 

 H. C. Cooper. 



Heidelbeeg. 



THE DAY OF THE WEEK. 



To THE Editor of Science : The statement 

 made in your issue of Science for October 18, 

 1898, by Mr. Edward L. Stabler, that ' I have 

 not found any published rule for the simple 

 problem of determining mentally the day of the 

 week without reference to a calendar or lengthy 

 table' leads me to send you the following 

 formula, which I have never seen in print, but 

 which is of so simple derivation that it may 

 well have been used by others than myself 



Let Y represent any year of the Gregorian 

 calendar and D the number of any day in that 

 year, e. g., for February 1, 1898, 1'= 1898 and 

 D = 32. Neglecting fractions, put 



r+i) + ^-^ + ^ = 7. + . 



where n is the quotient and r the remainder ob- 

 tained by dividing the first member of the 

 equation by 7. The remainder r then repre- 

 sents the number of the day of the week, e. g., 

 if r = 1 the given date falls on Sunday, etc., 

 and if the division is exact, ?• = 0, it falls on 

 Saturday. For the date given above we have 



Y 1898 



D +33 



(r— 1) /4 + 474 



(r— i)/ioo— 18 



(r— 1)/400+ 4 

 7)2390 



341 



3 = Tuesday. 



