66 Astronomy. 



ANOMALY IN THE FIGURE OF THE EARTH. 



So many ships touch at Madeira, and take a new departure 

 from it, that the longitude of the island is a matter of consi- 

 derable importance. Dr. Tiarks was therefore sent out by 

 die Board of Longitude to ascertain it, with sixteen watches, 

 in the summer of 1822 ; and a remarkable circumstance occur- 

 red, which was not within the object of his original mission. 

 For, in going from Greenwich to Falmouth, a difference of 

 longitude was found equal to 20' 11 ""49; and, in returning 

 from Falmouth to Greenwich, a difference of 20' 11 "'13. Now 

 the difference, as determined from the Trigonometrical Survey 

 (given hi the third edition of the requisite tables), is only 20' 

 6'*9; and this variation made it expedient to engage Dr. 

 Tiarks to verify his observations in the Channel. He was 

 furnished with twenty-nine chronometers, and was employed 

 from the latter end of last July till the middle of September 

 in sailing between Dover and Falmouth. His results are as 

 follows: 

 Longitude of Dover station h 5' 1 7"*54 E. 



Portsmouth Observatory . 4 24 '77 W. 



Pendennis Castle .... 020 10 '85 W. 



Madeira 1 7 39 -08 W. 



From hence it is clear that the figure of the earth must be 

 somewhat different from that assumed for determining the lon- 

 gitudes from the Trigonometrical Survey, and that about 5" 

 must be added, in the latitude of the Channel, for every 20' 

 of longitude which is deduced from it. — Ediub. Phil. Joum., 

 vol. x. p. 179. 



REMARKS ON PROFESSOR STRUVE's OBSERVATIONS TO DETER- 

 MINE THE PARALLAX OF THE FIXED STARS. BY J. POND, 

 ESQ., ASTR. ROYAL. 



Of the various attempts to discover the parallax of the fixed 

 stars, the observations of Professor Struve must be regarded 

 as among the best and most judicious. [Obs. Vol. II. III.] 



His object is, by means of an excellent transit instrument 

 furnished with seven wires, to determine the sum of the paral- 

 laxes of several fixed stars, differing nearly 12 hours in right 

 ascension from each other. 



The results which he obtains seem to verify a remark which 

 I have often had occasion to make; that in proportion as any 

 improvement takes place either in our instruments or our pro- 

 cesses, the resulting parallax becomes proportionally less. 



Of fourteen sets of opposite stars thus compared, Mr. Struve 

 finds seven, which give the parallax negative : this circum- 

 stance alone should suggest great caution in attributing to the 



effects 



