14-0 Mr. Bevan's Observations on the Heights of Places 



In him the blindness has been invariably to his right of the 

 centre of vision, and, from want of due consideration, had 

 been considered as temporary insensibility of the right eye ; 

 but he is now satisfied that this really is not the case, but that 

 both eyes have been similarly affected with half-blindness. 

 This symptom of his indigestion usually lasts about a quarter 

 of an hour or twenty minutes, and then subsides, without 

 leaving any permanent imperfection of sight. 



I have not seen the subject of the 5th case ; but I am in- 

 formed that he has had many returns of this affection, gene- 

 rally attended with head-ach, and always lasting about twenty 

 minutes, with very little variation. 



XXIII. Observations on the Heights of Places in the Trigo- 

 nometrical Survey of Great Britain, and upon the Latitude 

 of Arbury Hill. By B. Bevan, Esq. Communicated by 

 Sir H. Davy, Bart. P.R.S* 

 'T'HE Trigonometrical Survey of Great Britain having from 

 ■*- time to* time engaged the attention of the Royal Society, 

 and circumstantial particulars of this great national under- 

 taking having occupied the pages of the Philosophical Trans- 

 actions, I beg leave to submit a few observations on that 

 subject to the consideration of the Society. 



The result of the survey, relative to the different sections of 

 the meridian, in this country, has not altogether proved so 

 satisfactory as might have been expected. 



I have lately examined the calculations affected by the ob- 

 servations made at Arbury Hill in the county of Northampton, 

 with some hope of discovering the means of reconciling the 

 anomaly in that part of the meridian. 



I have been at the expense of having the height of this sta- 

 tion determined by accurate levelling to the Grand Junction 

 Canal ; from which, and the known difference of level of the 

 various canals connected with this, I have been able to find 

 the relative height of this station, with most of the important 

 objects in the counties of Northampton, Buckingham, and 

 Bedford. 



From this operation of levelling, I found the country to the 

 north of Arbury station, suddenly to fall about 400 feet, and 

 continue at this depressed state for 9 or 10 miles. Such a 

 defect of matter, to the north of the station, was in itself a 

 strong ground for supposing a deflection of the plumb-line to 

 the southward. To ascertain if this supposition were sup- 

 ported by the trigonometrical operations, I calculated the la- 



* Fiomlhc Philosophical Transition for 1823, Part I. 



titude 



