4/0 Scientific Intelligence. [Dec. 



disappear. Here is one supposition certainly entitled to examina- 

 tion. Nor do I think that the trouble and expense of repeating the 

 observations at Arbury Hill would be great. No, says Dr. Gregory, 

 the instruments were so good that such an error was not possible. 

 Dr. Maskelyne, who understood observing fully as well as Dr. O. 

 Gregory, used to say that he did not think that the best instruments 

 would warrant a nearer approximation to the truth than 5" ; so that 

 what Dr. Maskelyne considered as the most accurate possible of 

 observations, Dr. Gregory thinks so inaccurate that it is impossible 

 to observe so ill. Yet he allows much greater errors to have been 

 committed by the French, in whose measurement, however, no 

 such anomaly appeared. So far from it being criminal in the Royal 

 Society to publish Don Rodriguez' paper, it was their duty to publish 

 it, in order to draw the attention of philosophers to the removal of 

 such an anomaly, if it be possible. 



2. Dr. Olinthus Gregory informs us that he wrote to M. De- 

 lambre on the subject of Don Rodriguez* paper, and that the 

 French astronomer had given it as his opinion that Don Rodriguez' 

 notion was untenable. Now it happens that M. Delambre has lately 

 published a System of Astronomy, in which he has given us his 

 opinion of Don Rodriguez' paper. I beg leave to lay the words of 

 this respectable writer before my readers : — " Posteriurement a la 

 mesure de Laponie, le Colonel Mudge mesura trois degres en 

 Engleterre, entre Clifton et Dunnose dans Tile de Wight. Par la 

 station d'Arbury il a partage son arc en deux parties presque egales. 

 II a soudivise ses parties en liant ses triangles a l'observatoire de 

 Greenwich et a celui du Lord Marlborough. On a ete fort surpris 

 que tous les arcs partiels compares entre eux, indiquassent un alonge- 

 ment. Mais en laissant de cote Greenwich et Blenheim, M. 

 Rodriguez a montre dans les Transanctions Philosophiques de 1812, 

 que l'arc entier s'accorde avec le demi-grand axe et l'aplatissement 

 qui resultent de nos mesures; qu'il suffirait ensuite de supposer une 

 erreur de 5" a la station intermediaire d'Arbury, pour que les deux 

 arcs partiels appartinsent au meme spheroide. 11 restera pourtant a 

 concevoir comment le beau secteur de Ramsden dont l'erreur etait 

 constant ou nulle aux extremities, a pu avoir un erreur different de 

 5" a la station intermediaire. Mais que ces anomalies proviennent 

 de l'instrument au des inegalites locales, ce qui parait n'etre pas 

 encore bien decide, il en resultera toujours que dans les operations de 

 ce genre il n'y a de euret? que dans les arcs d'une grande etendre, tel 

 que celui qui va de Dunkerque a Barcelone ou Formentera, ou 

 l'erreur, quellqu'en puisse etre la cause, se trouve divide par un 

 plus grand intervalle. Dans les arcs trop petits et contigus, l'erreur 

 inevitable des observations doit avoir un trop grande influence sur 

 le resultat, qui ne peut repandre aucun jour sur la question de 

 l'aplatissement. "* ^_ 



* Astronomie Theorique ct Pratique. Par M. Delambre, 1814, vol. ii't, p. 325. 



