82 PEOCEEDIXGS OF THE REGENTS. 



The following remarks relative to tliis letter have been received from Professor 

 Guyot, to -whom it was submitted : 



"I return to you, witli my thanks for its communication, the interesting letter 

 of Dr. Engelmann. I had become acquainted with a part of that information 

 by a letter from himself. It is exceedingly gratifying to see that interesting 

 field of labor beginning to be explored. I trust that Dr. Parry will be able to 

 continue his useful investigations. 



"A great desideratum for the mountain measurements of the far west is the 

 determination of some points near the base of the great chains with some degree 

 of accuracy. We would obtain such points by a few regular barometric stations. 

 Could not an observer be found in Denver or Colorado City, for instance, who 

 would at the same time furnish suitable corresponding observations for measure- 

 ments in the mountains, which are indispensable for the accurate determination 

 of the high peaks of the Eocky mountains'? It is rather provoking to have the 

 consciousness that we do not know the true altitude of any point in these 

 2,000 miles of inland country, within one or two hundred feet, to say the least. 



" I suppose that the barometric correction by Plautamour, mentioned in the 

 report of the proceedings of the British Association, relates to the influence of the 

 hour of the day at which barometric measurements are made, as derived from 

 the means of St. Bernard and Geneva. It is the correction the amount of which 

 I tried to determine in the latitude of the Black mountain and elsewhere, and 

 which I apply in all my measurements. It amounts to ^ L_ of the dilference 

 measured, in the hottest part ox the day, above the mean, or -^^ if we take the 

 daily extremes. It is thus of considerable importance, though usually neglected. 

 I think, however, that the whole needs a considerable revision. Temperature 

 is the main cause, but the diurnal variation of pressure also comes in with con- 

 trary effects." 



United States National Observatory, 



Washington City, January 8, 1862. 



Dear Sir: You are, I believe, aware that for some time past I have bceo 

 eno-agod in investigations relative to Biela's comet. In the course of these 

 investigations I have collected and discussed all the observations that could be 

 found for each of the recorded six appearances, and, by help of independent 

 elliptic elements for each, have digested these observations into a series of 

 twenty-five normal places, extending though, with wide intervals, from 1772 to 

 1852. I have also computed rigorously the effect of planetary perturbations 

 from 1846 to 1858, and am now engaged in continuing this computation to the 

 next return in 1865. JMoreover, I have carefully studied the relative motions 

 of the two nuclei into which the comet is now divided, and find that the time 

 and place of their separation can be indicated with a good degree of approx- 

 imation, thus limiting the field of possible causes of the catastrophe. 



It was my expectation, at the outBet, to have extended the calculation of 

 perturbations over the whole interval from 1772, so as to unite, if possible, by 

 a single theory, all the observed places of the comet ; but a nearer contempla- 

 tion of this task, and a little actual trial, show that with my present ofiicial 

 duties this would be a work of many years. It has occurred to me, however, 

 that it would be in accordance with the plans of the Smithsonian Institution, 

 and in keeping with the generous interest it has always shown in scientific 

 investigations, to assist in this work by enabling me to employ a computer, to 

 whom can be intrusted the more mechanical details of calculation. I venture, 

 then, to suggest this proposition to you, and if, as I would fain hope, it should 

 meet your approval, and you authorize me to enter into such an arrangement, 



