135 



(correspondence with Sir G. Airy), the meaning of words, and questions 

 about lost people. 



A few extracts from some of these letters will suffice to show how 

 Otley was employed, and how he was thought of by those with whom he 

 came in contact. 



In 1818, Otley corresponds with Mr. Greatorex of Portland Place, 

 who sends him the heights of several stations visited by them together, 

 as calculated from their barometrical observations, giving at the same 

 time the details of his calculations. 



Throughout his long life he interested himself in the heights an 

 names of mountains, and the two following letters bear upon this point, 

 the one by Otley being written in his eighty-ninth year. 



From Captain Gosset. 



Ordnance Map Office, Southampton, 

 March 26th, 1853. 

 Sir,— 



Your note relative to the datum plane for the LeveUing of the Ordnance 

 Maps has been forwarded to Colonel Hale, R.E., by whom I am directed to reply 

 to your questions. 



The datum plane is mean line of the Sea Level (obtained from a large number 

 of tide observations) at Liverpool. The six-inch Ordnance Survey began in Lanca- 

 shire, therefore Liverpool was selected. The mean line has been adopted because 

 it is the most steady point in'Tides. The mean between a High and Low water 

 mark at a Spring Tide is nearly the same point as the mean between High and Low 

 water mark at any other tides taken by pairs of tides. 



You are coloring some of the contours ; permit me to remark that to color 

 those of the same altitude one color, those of a second altitude another color, and 

 so on, gives information to the eye from end to end of a sheet at a glance. 



Your obedient servant, 



W, DmscoH 60SSET, 



Captain R.E. 



From Mr. Otley to Captain Gosset. 



Keswick, July 13th, 1854. 



Your kind letter of March 26th, 1853, in answer to my enquiry respecting the 

 Map of Coniston Fells, I am emboldened to offer to your notice a few of the 

 observations that I have made on the subject, chiefly relating to names. I am glad 



