244 



SCIENCE 



[N. S. Vol. XLIV. No. 1129 



well founded that there is room for alternative 

 superstructures beside that which Chamberlin 

 here presents. 



The previous paragraph has dealt with alter- 

 native possibilities; on page 178, however, an 

 erroneous diagram of stress-differences due to 

 the weight of second harmonic inequalities is 

 taken from G. H. Darwin. The original paper 

 was published in 1882. About a year later 

 Charles Ohree pointed out an error in Darwin's 

 procedure which led Darwin to publish a cor- 

 rection in 1885. The correct solution is given 

 in Darwin's Scientific Papers, Vol. II., pp. 

 459-481, 1908. The erroneous diagram indi- 

 cates a tidal force eight times greater at the 

 center than at the surface. A corrected dia- 

 gram would show the tidal stress at the poles, 

 on the equator, and at the center in the ratio 

 of one to three and eight. On the equatorial 

 surface the stress due to either tides or to 

 lack of adjustment between oblateness and 

 rotation period is therefore not one eighth but 

 is in reality three eighths of the amount at the 

 center. The maximum stress-difference at the 

 equator is, however, not in a vertical but is in 

 the horizontal plane. There is doubt if tidal 

 stresses could ever have been an effective agent 

 in kneading liquid matter out of the earth's 

 body, since the forces are relatively small and 

 the pressure gradient due to that cause is very 

 much smaller still. On the other hand, if the 

 moon were much nearer the earth in primor- 

 dial times the tidal stresses may have risen to 

 an important magnitude. 



But in closing we must not look at this or 

 that detail, nor at this or that chapter. To 

 gain a proper appreciation of the value of the 

 investigations which are condensed in this 

 volume we must compare the present state of 

 thought upon the general subject with that 

 of twenty years ago, before Chamberlin had 

 begun to publish upon the hypotheses of earth 

 genesis. Measured by that perspective this 

 volume is seen to represent an advance in 

 thought on this subject so great that the names 

 of Chamberlin and Moulton must rank high 

 among those scientists who have dealt con- 

 structively with that vast, vague and remote 

 problem — the Origin of the Earth. The sub- 



ject of earth genesis is now fairly on the road 

 to scientific investigation in place of philo- 

 sophic speculation. Joseph Barrell 



PROCEEDINGS OF THE NATIONAL 

 ACADEMY OF SCIENCES 



The seventh number of volume 2 of the 

 Proceedings of the National Academy of Sci- 

 ences contains the following articles : 



1. On the Mobilities of Gas Ions in High 

 Electric Fields: Leonard B. Loeb, Byerson 

 Physical Laboratory, University of Chicago. 

 The results, though at variance with those 



of most observers at low pressures for negative 

 ions, are in good agreement with recent re- 

 sults of Wellisch, and likewise lead to the 

 conclusion that the "cluster" theory is no 

 longer tenable. 



2. The Relation of Myelin to the Loss of 

 Water in the Mammalian Nervous System 

 ■with Advancing Age: Henry H. Donaldson, 

 "Wistar Institute of Anatomy and Biology, 

 Philadelphia. 



There is no evidence that the cell bodies 

 and their unsheathed axons suffer any signifi- 

 cant loss of water; the progressive diminution 

 in the water content of the brain and spinal 

 cord is mainly due to the accumulation of 

 myelin, the formation of which is a function 

 of age, the most active production occurring 

 during the first twentieth of the life span. 



3. Differential Mitoses in the Germ-Cell Cycle 

 of Dineutes nigrior: B. W. Hegner and C. 

 P. Bussell, Zoological Laboratory, Univer- 

 sity of Michigan. 



The most conspicuous difference that we 

 have discovered between the origin of the oocyte 

 in Dineutes nigrior and in Dytiscus is in the 

 number of differential mitoses; in Dineutes 

 nigrior there are only three whereas in Dytis- 

 cus there are four. 



4. Some Minerals from the Fluorite-Barite 

 Vein near Wagon Wheel Gap, Colorado: 

 Esper S. Larson and Eoger C. Wells, U. S. 

 Geological Survey, Washington, D. C. 



A description of specimens of the unusual 

 mineral gearksutite of a peculiar kaolinite and 

 of a new fluoride-sulphate, creedite. 



