544 



.VA TURE 



[October i, 1908 



(i) If onh' an approximate azimuth is required, the 

 best means of determining it is by fixing- the direc- 

 tion of the sun or a star when it has the greatest 

 altitude. This direction, of course, defines the astro- 

 nomical meridian, as all heavenly bodies cross it when 

 they are at their greatest altitude. 



By using stars of both high and low altitudes a 

 gieater exactness can be obtained, but, after all, the 

 method only gives a first approximation, as its weak- 

 ness lies in the very slow change of altitude as the 

 meridian is approached. 



(2) A much more accurate method is that of observ- 

 ing the azimuth of a star when at the same altitude 

 east and west of the meridian. If the mean of the 

 two readings given by the azimuth circle be taken, 

 the resulting reading indicates the direction of the 

 meridian. 



(3) To find the meridian line by means of the polo 



importance, for in such work, if accuracy is required, 

 as it should be, one setting and one reading are of 

 little use. 



Norman Lockver. 



THE HORNED DINOSAURS.' 



FRO^NI time to time mention has been made in the 

 columns of N.\ture of contributions to our know- 

 ledge of what are perhaps the most wonderful mem- 

 bers of a wonderful order, namely, the horned dino- 

 saurs, or Ceratopsia, of the -American Upper Creta- 

 ceous, the last of such notices relating to Mr. Lull's 

 conclusions to be drawn with regard to the cranial 

 muscles of the typical forms from the studv of the 

 skull. In the present sumptuously illustrated volume, 

 which has a melancholy interest as being mainlv the 

 work of an exceedingly talented and promising 





h 



Kestor.ition of a Horned Dinosaur (Triceratops), with an Iguanodont (Trachodon) in the distance. From Hatcher's "Ceratopsia." 



star is a simple and accurate method, as a value can 

 be obtained at any time at night by a simple altitude, 

 provided the time of observation is known. 



Should there not be sufficient time to take the 

 necessary observations, the true bearing of the sun 

 and also some star can be obtained by inspection from 

 Birdwood's azimuth tables. 



If we employ the sun in place of a star, its change 

 of declination during the interval between the observa- 

 tions must be talcen into account. 



It is not alone with regard to azimuth that the 

 results obtained by a theodolite far surpass all others 

 in accuracy, as all magnetic difficulties are overcome, 

 and larger circles give us closer and more accurate 

 readings. 



In altitude observations the fact that the observing 

 telescope can be rever.sed and swung round so that 

 all sources of errors of the horizontal plane of the 

 instrument can be eliminated is a matter of equal 



N"0. 2031, VOL. 78] 



palaeontologist who did not live to earn the full re- 

 ward of his labours, we have a full description of all 

 that is known with regard to the osteology, relation- 

 ships, and classification of these wondrous reptiles, 

 together with notes and speculations (by .Mr. Lull) 

 regarding their distribution, phylogeny, and probable 

 habits and environment. 



In his preface Mr. Hatcher, we are glad to observe, 

 bore testimony to what we owe to the late Prof. O.C. 

 Marsh in the matter of our knowledge of the Cera- 

 topsia. To a large extent his generositv " made it 

 possible to bring together the collections upon which 

 this volume is based. Nor did his contributions to the 

 subject end here, for, as appears on the title-page, the 

 present memoir was based on his preliminarv studies, 

 and although he left no maouscript aside from his 



1 "The Ceratopsia." By J. E. Hatcher. Edited and completed by 

 R. S. Lull. Pp. .\xx + ioo; plates i-lii. (Washington: U.S. Geol. Survey. 

 Monograph .\li.\., 1907.) 



