Observations of the Appearance of the Cornel. 3 1 1 



to the public his first trials; and therefore, whatever dif- 

 ferences exist between his numbers and ours may have been 

 obtained at his second calculation. The inaccuracy of the 

 first he expressly admits in his letter to the editor of the 

 Moiiiteur, which' begins in the following manner : " Havinjr 

 been requested to correct my first determination," &:c. I 

 wish it to be understood, however, that the appearance of 

 his statement has not shaken, in the least degree, the con- 

 fidence I humblv conceive due to our own results. The 

 observations from which these are derived were performed 

 with the instruments of Troughion ; instruments unques- 

 tionably superior to any. other in the world. But we have 

 still more direct assurance of the accuracy of our observa- 

 tions, by compajing them to the numbers which have been 

 published from the highest authority (the astronomer royal) 

 in thcPhifosophical Magazine of last month. The longi- 

 tudes of the comet, detcrmmed at Greenwich and Glasgow 

 Observatories, coincide to the fraction of a minute. 



The time of the perihelion passage may be considered as 

 pretty accurately fixed, either lor Sept. 12 or 9, or, as is more 

 probable, at some intermediate period. From this we can 

 fullv explain some of the phienomena generally remarked. 

 From the yth, as stated in the Glasgow papers by a cor- 

 respondent, the comet was observed to increase cor.sider- 

 abl'y both in brilliancy and in the apparent magnitude of 

 the coma, but particularly oF the tail, in the course of 

 eight davs. This verifies very happilv the observation of Sir 

 Isaac Newton, that it is not till immediately after the peri- 

 helion passage, that comets acquire their maximum of lustre 

 and of size. The enlargement therefore uniformly takes 

 place at that time, whether the comet is coming nearer us 

 or moving in the opposite direction. The quantity ot in- 

 crease due to its approximation alone, in six or eight days, 

 can be calculated, and we know that there is no instrument 

 in Scotland capable of measuring the change of apparent 

 magnitude produced by this cause. Whether the exquisite 

 micrometer of Troughton, applied to our great Herschelian 

 telescope, may show any d fference, I shall be able to ascer- 

 tain in a few days, as that instrument is laicly dispatched 

 from London for us. 



I must acknowledge, however, that I entertain very slen- 

 der hopes of success "in this kind of observation on a minute 

 body surrounded with such a nebulosity, and at a distance 

 from us much greater than that of the sun. It has been 

 said, that this comet was ascertained to be the same with 

 that of 1661. The two are as diflerent as can b« imagined 

 U4 in 



