602 Royal Astronomical Society Eocperiments ivith 



might have been expected from so fine a series of observations. 

 The author, however, feels confident that the results are correctly 

 derived, from the pains taken to ensure accuracy : and the whole 

 is given in a detailed shape, in order that any suspected error may 

 be more readily detected. 



An Account of some Experiments made with an Invariable Pen- 

 dulum, at the Cape of Good Hope. By T. Maclear, Esq. 



When Mr. Maclear was appointed Astronomer at the Cape of 

 Good Hope, he was desirous of repeating the experiments there 

 with an invariable pendulum ; but it was some time before he had 

 sufficient leisure to prosecute this measure. The pendulum had 

 been previously swung in London by Mr. Baily, and also after its 

 return to this country. The method of proceeding in such cases is 

 so similar, and has been so often described, that it is unnecessary 

 to enter further on that part of the subject. The result of these 

 experiments shows, that, on the assumption that the pendulum 

 made 86400 vibrations in London, in a mean solar day, at the tem- 

 perature of 62° in vacuo, and at the mean level of the sea, it made 

 only 86332"92 vibrations, under the same circumstances, at the 

 Cape of Good Hope ; which is almost identical with the experi- 

 ments of Mr. Fellows, and differing very little from the experiments 

 of Captain Foster and Freycinet. A new pendulum, consisting of 

 a thick brass bar, without any bob, and furnished with four knife 

 edges, is about to be forwarded to Mr. Maclear, which he proposes 

 to swing at the principal stations of the triangulation that is now 

 carrying on in that colony. 



An Account of some Experiments made with three Invariable 

 Pendulums, by Lieut. Murphy, R.E., during the late Expedition 

 down the Euphrates. By Mr. Baily. 



When Colonel Chesney undertook the expedition down the Eu- 

 phrates, three invariable pendulums were placed under his care, for 

 the purpose of their being swung at positions more inland than had 

 been liitherto practised. Two of these pendulums (iron and copper) 

 belonged to this Society, and the other (brass) to the Admiralty ; 

 and they are the same that were taken out by the late lamented 

 Captain Foster. They had been previously swung in this country, 

 before the expedition just mentioned, by Mr. Baily, and also subse- 

 quent thereto. Only two places presented favourable opportunities 

 for swinging these pendulums during the expedition : the first, at 

 Port William, near Bir, on the Euphrates ; and the other, at Bussora. 

 The experiments were made by Lieutenant Murphy, and were con- 

 ducted with his usual caution and ability : the details are recorded 

 in printed skeleton forms, with which he was furnished previous to 

 his departure ; but none of the computations were made till after 

 Lieutenant Murphy's decease. The reductions have since been 

 made by Mr. Baily, on the same data as those already mentioned in 

 the seventeenth volume of the Memoirs of this Society. On the as- 

 sumption that each of these pendulums made 86400 vibrations in a 

 mean solar day in London, at the temperature of 62° in vacuo, and 

 at the mean level of the sea, it is found that they respectively made 



