242 



SCIENCE. 



[N. S. Vol. III. No. 59. 



two degrees of declination. The corrections 

 are given for the epoch 1755, when they depend 

 on Auwers-Bradley; 1875, when they depend 

 on Pulkowa; 1880, depending on Greenwich; 

 1885, on Pulkowa; and finally, 1890, depending 

 on Greenwich. The corresponding corrections 

 for 1847, which is the mean epoch of Boss' 

 system, are taken as zero. From the fact that 

 these corrections to Boss do not vary uniformly 

 with the time. Prof. Newcomb draws the con- 

 clusion that Bradley's observations must be in- 

 consistent with the truth, which seems to imply 

 that they are to be accorded no weight in form- 

 ing a normal system. Yet we may well ask 

 whether the numbers given by Prof. Newcomb 

 are accurate enough to furnish any information 

 of reliability. In his zone A the correction to 

 Boss for 1755 is -2".23. But the ten numbers 

 of which this is the mean have a range of no 

 less than 4''. 00. So we can hardly escape 

 the conviction that the whole conclusion may 

 be vitiated by a large error in a particular 

 star. That this has occurred is not altogether 

 impossible. For zone B the corresponding 

 mean is 0".27, with a range of 2". 30 in 

 the ten numbers whose mean has been taken. 

 We cannot regard conclusions based upon evi- 

 dence so discordant as final. It is to be noted 

 also that only one of the twenty stars used by 

 Prof. Newcomb is to be found in Boss' mean 

 system. The other nineteen stars are among 

 those taken by Prof. Boss from the catalogues 

 which were not used in forming the mean sys- 

 tem, but which were reduced to the mean sys- 

 tem by the aid of systematic corrections. In- 

 deed in all researches with Boss' system we are 

 met at every step by the insuperable difficulty 

 that his original mean system does not contain 

 stars enough to get rid of casual errors in indi- 

 vidual stars. While therefore we agree with 

 Prof.Newcomb's final conclusion that the system 

 of Auwers cannot be regarded as definitive, and 

 that it requires revision, we wish to point out 

 that the same is true of the Boss system. And 

 finally we wish to repeat our former statement 

 that it is not at present practically possible to 

 employ the Boss system, because the reductions 

 to that system for the recent accurate cata- 

 logues have not been published. This has been 

 done with care for the Auwers system, and un- 



til it has been done for the Boss system astron- 

 omers wishing to deduce for any purpose the 

 most accurate declination of a star from all the 

 catalogues will have to use the Auwers sys- 

 tem. H. J. 



THE AGE OF THE PHILADELPHIA BEICK CLAY. 



In Prof. Salisbury's last excellent report on 

 the Surface Geology of New Jersey some of 

 the most important points are likely to be over- 

 looked by reason of the different names applied 

 to the same formation by successive investi- 

 gators. Fully to appreciate the light which 

 Prof. Salisbury's investigations shed upon some 

 of the points recently under discussion, it is 

 necessary, after the manner of the mathema- 

 ticians, to substitute in one equation its equiva- 

 lent in another. 



What was formerly referred to as the ' Phila- 

 delphia Brick Clay ' was later correlated with 

 the 'Columbia.' This, however, is now prop- 

 erly described by Prof. Salisbury in the New 

 Jersey report (from its place of greatest develop- 

 ment in that State), under the name of 'James- 

 burg,' of which he says there can be no doubt 

 that it corresponds to the Columbia. This de- 

 posit as developed on the Pennsylvania side of 

 the Delaware River, from Philadelphia to Tren- 

 ton, was very carefully studied fifteen years 

 ago by the late Prof. Carvill Lewis, his views 

 regarding it being embodied in various papers 

 published about that time and finally in the 

 last chapter of Abbott's 'Primitive Industry' 

 (pp. 524-527), published in 1881. His conclu- 

 sions were "that this clay may be assigned to 

 a period when the land stood 150 feet or more 

 below its present level, and when the cold 

 waters from the melting glacier bore ice rafts 

 which dropped their boulders. ' ' 



After going over much of this field with Prof. 

 Lewis, I adopted these views and incorporated 

 them into my various references to the subject. 

 (See especially Proc. of the Boston Soc. of Nat. 

 Hist., Jan. 19, 1881, p. 141; Ice Age in North 

 America, p. 523, and later in Am. Jour. Sci., 

 March, 1894, pp. 180, 181.) It is gratifying to 

 see that Prof. Salisbury's studies upon the New 

 Jersey side of the river lead him to substan- 

 tially the same conclusions. First, in opposi- 

 tion to Mr. XJpham, he now holds that (p. 126) 



