Reply to Mr. Grubb's Criticisms on the Equatorial Coudé of the Paris Observatory

Abstract

I HAVE just received the last number of the Scientific Transactions of the Royal Society of Dublin, containing a description of an instrument analogous to the equatorial constructed on a principle which I published in 1871 in the Comptes Rendus. Since it seems to me indispensable after I have studied Mr. Grubb's memoir to reply to it publicly, I beg you to insert this note in NATURE. In order to give greater importance to the modifications imagined by himself, the author, Mr. Grubb, submits the instrument imagined by me to a very severe criticism, and attributes very severe defects to it. There is no doubt that there is a considerable difference between the instruments in question. One of them, in fact, as experiments carried on during two years have proved, lends itself to the execution of all possible astronomical researches under the best possible conditions for securing precision, while the other, according to the description given in the publication above cited, renders impossible a very great part of the researches to which an equatorial is specially destined. Further on I shall insist on this difference, but I wish first of all to reply to Mr. Grubb's objections and to show that they are in all points contrary to the fact.