ASTRONOMY. . 409 



by its i^reat^T accuracy. Professor Biikliuyzen lias, however, endeav- 

 ored to utilize the eutire mass of observatious at his disposal, so as to 

 avoid the sources of error to which the other methods are liable, and 

 he possesses a grasit advantage over earlier investigators, in having ac- 

 cess, not only to the numerous observations made in 1877 and 1879, but 

 also to the great series of more than 200 drawings which Schroeter had 

 prepared for his projected ''Areographischen Beitriige," and which be- 

 coming the property of the University of Leyden in 1876, was edited 

 and published by Professor Bakhuyzen in 1881. Professor Bakhuyzen, 

 in the reduction of these drawings, has adopted provisionally Schftipa- 

 relli's position for the pole of Mars— E. A. 317° 40'-0, Decl. 53° 25'-^, 

 mean equinox of 1833-0 — and Proctor's rotation period — 24'' 37™ 228-74 — 

 and deduces corrections to these elements from a comparison of the re- 

 sults obtained by reducing the various observations at his command 

 with them. His first step is, from a discussion of the drawings of Kai- 

 ser, Lockyer, Lord Rosse, and Dawes, made during the oppositions of 

 of 1862 and 1864, to obtain the time of transit on January 1, 1863, of 

 his adopted prime meridian over the Martial meridian, which passes 

 through the earth's north pole, choosing as his prime meridian the one 

 which lies 2° to the east of the center of Miidler's point a, correspond- 

 ing almost exactly to Schiaparelli's Fastigium Aryn, or to Proctor's 

 Daives Forked Bay, he finds the time of transit over the meridian pass- 

 ing through the north pole of the earth on January 1, 1863, to be 20'' 

 27™ ± 4-0'", Berlin M. T. The areographic longitude of the center of 

 the Oculus, the conspicuous circular spot, called by Green the Terbi/ Sea, 

 and by Schiaparelli Lacus Solis, will be, with this prime meridian, 90o-87. 

 The second section contains the determination of areographic longitudes 

 of ten of the most conspicuous and easily identified markings on the 

 surface oii Mars as inferred by means of the above elements from the 

 drawings of various observers from the time of Hooke and Huygens 

 up to 1879. For the last-named year only Schiaparelli's observations 

 are used, but for 1877 there is an abund^int supply, there being availa- 

 ble, besides the observations of Schiaparelli, the drawings of Lohse, 

 Green, Dreyer, and Niesten. Beer and Miidler's drawings aflord mate- 

 rial for 1830, Herschel and Schroeter give a very full series from 1777 to 

 1803, and Huygens and Hooke supply a few drawings from 1609 to 

 1683, from which the longitude of Miidler's /, the Kaiser or Hourglass 

 Sea, Schiaparelli's Syrtis Major, can be inferred. These logitudes are 

 discussed in the third section, and a corrected rotation period is ob- 

 tained of 24^' 37™ 228-66 ± 0«-0132, a value exceedingly close to the mean 

 of the best previous determinations, which are as follows : 



h. m. 9. 



Kai8er,1864 24 37 22-62 



Kaiser, 1873 -591 



Schmidt, 1873 -57 



Proctor, 18G8 -735 



