30 



SCIENCE 



[N. S. Vol. XLIII. No. 1097 



rents in the use of the latter instrument, 

 tliougli due precautions must have been taken 

 to avoid any possible error from this source. 

 It is unfortunate that the Kelvin type of gal- 

 vanometer still has to be retained, in most 

 cases at least, on account of the stray field 

 produced by the permanent magnet of the 

 moving coil galvanometers. Dip values ob- 

 tained with the earth inductor are now con- 

 sistent to within about one minute of arc. The 

 corrections for individual dip needles usually 

 amount to very much more than this. 



The tabulated results of observations are 

 comprised in about forty pages. The data in- 

 clude geographical position, date, horn-, and 

 values of declination, dip, and horizontal in- 

 tensity, for a very large number of stations in 

 all of the continents, the antarctic regions, 

 and chief island groups. No reduction of 

 values to a common epoch is attempted. In- 

 tensities are given in C.G.S. imits. Physicists 

 may well question the necessity of introdu- 

 cing, at the headings of columns of horizontal 

 intensity, the special symbol r, which, we are 

 told, represents one C.G.S. unit. In the al- 

 ready highly be-symboled state of science 

 would we not better rest content with that 

 " perfectly good " name for the C.G.S. unit, 

 which is also a reminder of the father of the 

 science of terrestrial magnetism, the gauss'i 



In connection with the land observations, 

 instrumental and other assistance has been 

 furnished in cooperation with various organi- 

 zations and expeditions. The Australasian 

 Antarctic Expedition and the Crocker Land 

 Expedition may be especially named. The ob- 

 servers' field reports are replete with notes of 

 interest to the geologist, botanist, biologist 

 and explorer. If one seeks information con- 

 cerning selection of firearms, feeding of 

 camels, defense against Bedawins, or canoe- 

 ing in the Canadian wilderness, he will find 

 it here. 



A valuable featm-e of the book is the detailed 

 description of the research buildings recently 

 erected near Rock Creek Park. The main 

 building is of fireproof construction, and so 

 stable that no perceptible vibration is trans- 

 mitted to the most sensitive galvanometers. 



even when the machinery in the basement is 

 running. For work demanding freedom from 

 magnetic disturbances, a separate non-mag- 

 netic building has been erected. Those inter- 

 ested in the building and equipment of labora- 

 tories of any kind will profit by a study of 

 these carefully planned structures. 



The only special researches recorded in this 

 volume are some miscellaneous observations 

 made in Samoa at the time of the solar eclipse 

 of April 28, 1911, and a very detailed descrip- 

 tion of the comparisons of magnetic standards 

 made at various observatories. The present 

 attainable precision in magnetic observations 

 may be learned from the statement that " the 

 corrections, on absolute standards, for the 

 declination and inclination may be in error 

 by O'.l or 0'.2 and for the horizontal intensity 

 by about O.OOOlff." 



W. G. Cady 



Wesleyan University 



SPECIAL ARTICLES 



SOME SUGGESTIONS ON METHODS FOR THE 

 STUDY OF NITRIFICATIONi 



During recent years the use of one gram of 

 dried blood, tankage, cotton-seed meal, bone 

 meal, etc., mixed with 100 gm. of soil, has com- 

 monly been employed in laboratory studies on 

 nitrification. In some cases as much as 2 per 

 cent, of these materials has been used. On 

 the other hand, a much smaller amount of 

 ammonium sulfate is usually added because of 

 its greater solubility and recognized toxicity to 

 the nitrifying organisms when present in ex- 

 cessive concentrations. The results are fre- 

 quently stated in terms of the absolute amounts 

 of nitric nitrogen formed rather than in per- 

 centages of nitrogen nitrified. Comparisons 

 and conclusions on the relative nitrifiability 

 of nitrogenous fertilizers are commonly made 

 on the basis of evidence obtained in this way. 



In the course of studies on nitrification at 

 the University of California Citrus Experi- 

 ment Station, the writer recently observed a 

 wide range of variation in the nitrification of 



1 Paper No. 20, Citrus Experiment Station, Col- 

 lege of Agriculture, University of California, River- 

 side, Calif. 



