OP THE EXPEDITION. XI 



observatories, and not small, portable ones. The futility of an attempt with others is well 

 pointed out in the correspondence. The procuring a suitable meridian circle will constitute, I 

 suppose, the greatest expense of the Expedition. Without entirely suitable instruments and 

 ample time for the observations, the Expedition would, of course, fail in accomplishing its main 

 purpose. 



" As is well pointed out in the correspondence, if the Expedition should result in showing 

 that no new strength could be given by this method to the value of the solar parallax, the indi- 

 rect results from other observations would be most valuable ; no similar expedition has ever 

 been barren of scientific results. In this view of the subject, meteorological and magnetical 

 observations should be combined with the astronomical observations. 



" I have no doubt that you can present a plan to the honorable the Secretary of the Navy so 

 well matured in its details, and so moderate in the expenditures required, that he will give it 

 that favorable consideration which the character of his mind insures to such objects, and that 

 if no untoward circumstances prevent, he will yield the plan so considered that hearty support 

 which he has always extended to similar proposals for elevating the scientific character of our 

 country." 



On the 18th December, Prof. Peirce informed me : " My long delay in answering your very 

 interesting communications relative to your proposed expedition for determining the solar 

 parallax demands a serious apology. I assure you most earnestly that it did not arise from a 

 want of sympathy with the scientific zeal and devotion which have prompted you to this ardu- 

 ous enterprise, nor from a want of appreciation of the importance of a new and more accurate 

 solution of a problem which is the basis of all astronomical measurement, and of which there 

 is now ci single isolated determination. I have delayed only that I might give the question a 

 calm, deliberate, and critical examination ; and, although fully aware of the little weight which 

 should attach to the opinion of one whose knowledge of practical astronomy is not derived from 

 personal experience, yet, since you have done me the honor of asking it, I have felt that I should 

 doubly err if I should answer without the most careful consideration, and should thus assist in 

 sending a friend and most valuable and highly accomplished officer upon so dreary an expedi- 

 tion with doubtful prospect of success. 



" A more accurate measurement of the sun's parallax in the method proposed by yourself 

 and Dr. Gerling cannot be regarded as inferior in importance to any problem in practical 

 astronomy ; and when sustained as to its practicability by the opinions of Dr. Bache and Mr. 

 Walker, whose authority upon the use of astronomical instruments can be weighed down by no 

 living testimony, there can be no further question as to its expediency. Most cordially, there- 

 fore, as well as deliberately, I send you iny humble testimony in favor of the enterprise you 

 have so nmch at heart and are so certain to accomplish, if it is, as it appears to be, within the 

 bounds of reasonable possibility. Let me entreat you, however, not to be satisfied with any- 

 thing inferior to the best possible instruments which art can furnish, for such instruments 

 seem to me absolutely indispensable, while the admirable observations which you have pub- 

 lished are a sufficient guaranty for the skill with which you will conduct their manipulation. 



"I shall bring the subject before the Academy early in the month of January, and shall be 

 greatly disappointed if a resolution is not immediately adopted in approbation of your project." 



When acknowledging the receipt of this personally complimentary letter, the arguments 

 which had weighed with me to desire such an expedition were detailed somewhat at length. A 

 note accompanied it, suggesting one or two obstacles almost sure to be encountered, and these 

 were replied to at the same time. A part of my letter was as follows: " Kemembering that 

 the solar parallax deduced by various astronomers from the transit of Venus in 1769 was* dis- 

 crepant at least 0".4; that, in a climate reputed as favorable as is (northern) Chile, we might 

 expect to obtain observations on at least two out of each three days; that therefore the ninety 

 days during which it is proposed to continue observations will give us sixty determinations of 

 the parallax, each of which might have a probable error of less than 1", and the resulting final 



