COMMUNICATION WITH THE PLANETS. 361 



relation vague. Prof. Zittell, of Municli, did not think the method of correlation 

 by plants accurate. Of animals, those of the land were most valuable. He spoke 

 of the difficulty of correlation in some countries where vertebrate animals are not 

 found in many of the deposits. Prof. Marsh agreed with the other speakers that 

 vertebrate animals afforded the best and most accurate material for correlation. 

 Prof. Charles D. Walcott spoke of the advances that had been made in the study 

 of correlation, and illustrated his positions by reference to the Cambrian strata of 

 North America. Prof. James Hall begged tiiat geologists in search of correlations 

 should not neglect physical methods, and described an early attempt at correlation 

 made by himself in ti'ying to connect the rocks of western New York with the 

 deposits of the West. 



COMMUNICATION WITH THE PLANETS. 



By M. AMEDEE GUILLEMIN. 



STRIKING discoveries in astronomy, of a character to excite 

 the public mind, have been rare in recent years. Those who 

 have kept in current with the work that has been done in that 

 science are not ready to believe that this is because progress has 

 not been made in it. As evidence of the new work accomplished 

 by its students, and potentially fruitful work, too, we cite the 

 preparation of a map of the sky, accomplished by the aid of pho- 

 tography, which gives the exact position of the stars to the four- 

 teenth magnitude. The co-operation of observatories certainly 

 assures the success of this immense work, which is now in process 

 of execution. La Nature has made known the beginnings and 

 has kept its readers in the current of the very minute and pro- 

 found preliminary studies, without which the undertaking of 

 operations of an extreme delicacy might have been compromised. 

 It has also made clear the importance of the results to be ob- 

 tained, and of the various consequences that would necessarily 

 accrue from them. The problems of parallax or of stellar dis- 

 tances, of the proper motions of the stars, of nebulae, the search 

 for minor planets and new comets, everything relative to the 

 constitution of sidereal systems, may, by an attentive study of the 

 plates of the new celestial maps, receive positive solutions. A 

 new horizon is thus opened to science. These are not sensational 

 novelties, like the appearance of a comet with a long, nebulous 

 tail, which attracts the attention of idlers to the sky ; but the im- 

 portance of astronomical observations is not measured by the 

 noise they make in the public ear. Yet, if the prize of a hundred 

 thousand francs, which an honorable lady has recently bequeathed 

 to the French Academy of Sciences, should be gained by some 

 one, the resultant emotion would be legitimate. To establish 

 voluntary and direct communication between the earth and a 



