ADVERTISEMENT. 



For more than twelve years past I have been preparing the material for the 

 publication of a work, on the part of the Smithsonian Institution, which it was 

 hoped would consist essentially of photographic views of the moon, so complete 

 and, it was expected (with the advance of photography), so minute, that the 

 features of our satellite might be studied in them by the geologist and the sele- 

 nographer, nearly as well as by the astronomer at the telescope. This hope has 

 only been partially fulfilled, for photography, which has made such eminent ad- 

 vances in the reproduction of nebulae and like celestial features, has indeed 

 progressed in lunar work, but not to the same extent as in other fields. The 

 expectation that such a complete work could be advantageously published for 

 this purpose has, then, been laid aside for the present. 



It has been decided to draw from the material prepared for this larger work, 

 some photographs taken at the Lick Observatory and the Paris Observatory, and 

 particularly some recently obtained by Professor Ritchey at the Yerkes Observa- 

 tory, for which I have to express the thanks of the Institution. These illustra- 

 tions are attached to the present paper by Professor Shaler, and may, then, be 

 considered to be a separate contribution by the Institution to the study of 

 selenography. 



Professor Shaler's memoir gives the results of personal studies carried on for 

 a third of a century. He has devoted about one hundred nights to telescopic 

 study of the moon with the Mertz equatorial of Harvard College Observatory, his 

 later researches having been chiefly by means of photographs at Harvard Uni- 

 versity, with which he has so long been connected. 



In accordance with the rule adopted by the Smithsonian Institution, the 

 memoir has been submitted for examination to a committee consisting of Dr. 

 George P. Merrill, Head Curator of Geology in the U. S. National Museum, 

 and Mr. C. G. Abbot of the Smithsonian Astrophysical Observatory. 



S. P. LANGLEY, 



SECRETARY. 



Smithsonian Institution, 



Washington, December, 1903. 



