'26 PHILOSOPHICAL TRANSACTIONS. [aNNO 1763. 



base very near 3 times greater than the former, and also the observation at Ro- 

 drigues, by which the base is nearly double of the former. But first he takes 

 notice, that in the Memoir by M. Pingre, before mentioned, the time of the 

 internal contact at the egress at Rodrigues is set down at O" 36" 49'. But in the 

 same volume there is an account of M. Pingr6's observation sent to the Royal 

 Academy before his arrival in Europe, and the time of the internal contact is 

 therein set down at O"^ 34"* 47'. Also in a letter from him to the Royal Society, 

 on his arrival in Europe at Lisbon, and dated the 6th of March, i762, and 

 which letter is printed in the Phil. Trans., vol. Hi, the time of the internal con- 

 tact is therein set down at O*" 34"* 47' true time. In another letter from him at 

 Lisbon to the Royal Society, dated 14th of March 1762, the time of the inter- 

 nal contact is again set down at O^ 34*" 47" true time, and he ends this letter in 

 these words, ' Notez que I'attouchement interne des bords s'est faite a 0*' 34™ 

 47*. Je fais cette remarque, parceque, vti la proximite de prononciation, qui 

 dans notre langue est entre 30 et 40, cette attouchement se trouvoit marque 10* 

 plutot qu'il ne devoit I'etre, dans une copieque j'ai faite pour mon usage: cette 

 erreur aura peut etre passe dans quelque autre copie. Mais, selon I'original, il 

 faut absolument lire O'' 34" 47'.' M. Pingre has no where, in the said memoir, 

 given any reason for this alteration of the time of the contact. If the inter- 

 nal contact at the egress at Rodrigues happened at O*^ 34™ 47"; and if this is 

 compared with the same observation at Tobolsk, the parallax of the sun comes 

 out = 7''.36. If the time of the contact at Rodrigues was at O** 35™ 47*, and if 

 this is compared with the same observation at Tobolsk, then the parallax of the 

 sun is found = 8".62. Again if the time of the contact at Rodrigues was at 

 O*^ 36™ 49', and if this is compared with the observation at Tobolsk, the paral- 

 lax of the sun will be found = 9".93. But to return. 



M. Pingre, in his letter to the Royal Society, dated at Lisbon March 14, 

 1762, sets down the time of the internal contact at the egress at O'' 34™ 47' true 

 time : and with regard to the time of the external contact expresses himself thus: 

 a O'' 53™ 18' le soleil a paru pendant 3 ou 4 secondes. Je n'ai pas vu le disque 

 ■du soleil bien ferme, il me paroissoit un peu alter^ au lieu de la sortie de Venus. 

 M. Thuillier ne voyoit rien avec la lunette de 9 pieds. J'ai de la peine k me 

 persuader que Venus soit sortie plutot.' It is plain from these words that M. 

 Pingre believed that the external contact did not happen before O*^ 53™ IB'. This 

 being allowed, let us compute the duration of the egress at Rodrigues, which we 

 shall find = 17™ 55\ It follows therefore that the internal contact happened at 

 0*" 35™ 23'. But this supposes that the observer could see the very last contact 

 of Venus with the sun's limb, the contrary of which Mr. S. has shown in a for- 

 mer paper on this subject. We are therefore certain that the external contact 

 happened later than O"^ 53™ 18', by several seconds, consequently the internal 



