540 



SCIENCE. 



[N.S. Vol. XVII. No. 431. 



Results of Ohservations with the Zenith 

 Telescope of the Flower Astronomical Ob- 

 servatory — from September 6, 1898, to Aug- 

 ust 30, 1901. By Charles L. Doolittle. 

 This is fourth in the series of publications 

 by Professor Doolittle of observations of lati- 

 tude. The first two contained observations 

 from April 1, 1876, to August 19, 1895, made 

 at the Sayre Observatory, Bethlehem, Pa.; 

 and the last two, from October 1, 1896, to 

 August 30, 1901, at the Flower Observatory 

 of the University of Pennsylvania. 



This series is of exceptional value as being 

 the earliest, as well as the most prolonged, 

 thus far made in the investigation of latitude 

 variations. It was begun seven years be- 

 fore the first proposal by Pergola at the ses- 

 sion of the International Geodetic Association 

 in Eome, that there should be an observational 

 test of the constancy of latitudes, and eight 

 years before Kiistner began his observations 

 whereby the discovery of variation was first 

 boldly announced as proved. Prom that 

 beginning, the series has continued, though 

 with some interruptions, until to-day. The 

 charts accompanying these four publica- 

 tions therefore show nearly a continuous 

 curve from December, 1889, to September, 

 1901. Sections earlier than 1889 may be 

 platted from the data given. The precision 

 of the observations is shown by a progressively 

 diminishing probable error for a single de- 

 termination of latitude ranging from ± 0".578 

 at the start with an inferior 'second-hand' 

 instrument, to ± 0".134 at present, with a 

 superior instrument of Warner & Swasey's 

 construction. 



Possessing fully as much interest as the 

 latitude curve, are the seven values of the 

 aberration constant, simultaneously deduced 

 as a by-product from the same observations, 

 viz., 



1889, Dec. 1, to 1890, Dee 13.. 20.448 ± 0.014 i 



1892, Oct. 10, to 1893, Dec. 27.20.551 .009 1 



1894, Jan. 19, to 1895, Aug. 19.20.537 .014 1 



1896, Oct. 1, to 1898, Aug. 16. .20.580 .008 J 



1898, Sept. 6, to 1899, Nov. 27.. 20.540 .010 1 



1900, May 5, to 1901, Aug. 30. .20.561 .008 1 



1901, Oct. 1, to 1902, Aug. 18. .20.510 1 



The last value is a preliminary determina- 

 tion announced previous to publication of the 

 observations on which it depends. The mean 

 of these values is 20".539, which differs only 

 0".016 from the mean of all determinations 

 thus far made by all methods included in 

 Dr. Chandler's discussion of this value {A. J. 

 529, 530), namely 20".523. 



In view of the high degree of accuracy now 

 attained in these observations and the pro- 

 longed period of time over which a single ob- 

 server has already extended them, though be- 

 set with singular difficulties, particularly in the 

 earlier portions of the series, it is a cause for 

 gratification that this fourth publication does 

 not mark the termination of Professor Doo- 

 little's work. It is still in progress, and as- 

 tronomers may confidently expect the publica- 

 tion of a fifth part, from August 30, 1901, 

 onwards. 



Herman S. Davis. 



A Treatise on Roads and Pavements. By 



Ira Osborn Baker, C.E., Professor of Civil 



Engineering, University of Illinois, etc. 



Pirst edition, first thousand. New York, 



John Wiley and Sons; London, Chapman 



and Hall, limited. 1903. 



According to the preface, ' the object of this 



book is to give a discussion, from the point 



of view of the engineer, of the principles 



involved in the construction of country roads 



and city pavements.' 



Prom this point of view we believe the work 

 of the author extremely well done. We also 

 believe that enough new matter and new ideas 

 have been introduced fully to warrant this 

 addition to the already large number of sim- 

 ilar works devoted to this general subject. 



Especially admirable is the arrangement of 

 chapters and of articles imder the chapters. 

 This arrangement gives the table of contents 

 unusual value, enabling the reader at a glance 

 to observe both the presence and absence of 

 the matter sought. 



While almost every possible subject is pres- 

 ent, we note with some surprise the absence 

 of any detailed discussion of cements, al- 

 though the use of cements in concretes and 

 concrete foundations and for other minor 



