90 Observations on the Measurement of 



sulphuric acid half as much more oxygen as in the sul- 

 phuruus. IF we couipare with this result the proportions 

 oF the combinations oF lead, it may be proposed as a ques- 

 tion For future examination, whether sulphur may not be 

 capable oFa lower degree of oxygcnization than it exhibits 

 in the sulphurous acid, or of a higher than in the sul- 

 phuric. [To be continued.] 



XIV. Observations on the Measi/rement of three Degrees of 

 the Meridian conducted in England by Lieut. -Colon el 

 William Mudge. By Don Joseph Rodriguez. 

 Communuattd by Joseph de Mendoza Rios, Esq. 

 F.R.S. 



[Concluded from p. 30.] 



X* ROM what has been above stated, it seems almost beyond 

 a doubt that it is to errors in the observations of latitude, 

 that the appearance oF progressive augmentation of degrees 

 towards the equator, as represented by Lieut. Col. Mudge 

 in his paper, are lo be ascribed, and that it is especially at 

 the intermediate station at Aibury Hill, that the observa- 

 tions of the stars are erroneous nearly five seconds, not- 

 withstanding the goodness of the instruments, and the skill 

 and care of the observer. But, before I insist further on 

 this he^d, I will answer one objection that may be made to 

 the principles of the method that 1 have pursued in this 

 memoir. 



Those astror>omers, who have hitherto undertaken the 

 measurement oF degrees oF the meridian, have deduced 

 their measures by siTnply dividing the linear extent by the 

 number oF degrees and minutes found by observation of 

 the fixed stars taken at the two extremities of the arc. This 

 is indeed the most simple that can be adopted; and it has 

 the advantage of being independent of the elliptic figure of 

 the earth, especia'-lv in arcs of small extent. The elements 

 dependent on this figure, are too uncertain to be employed 

 in calculating the angular intervals in the short distances 

 between successive stations, even as a means of verification, 

 without ri^k of cornmiiting greater errors than those to 

 which astronomical observations can be liable. Accordingly 

 one cannot safely make any use of it in cases where great 

 accuTvicy is required. 



I must admit the justness of this objection, and must 

 therefore show the extent to which it really applies to the 

 present subject. 



In the first place, I may suppose, thai in consequence of 



V some 



