BEDFORDSHIRE: SURVEYING 109 



different observers, while allowance had also to be made for 

 height above the sea-level, to which all the distances had to be 

 reduced. In this way, starting from any one base, the lengths 

 of the sides of all the triangles were calculated, and ultimately 

 the length of the other bases ; and if there had been absolutely 

 no error in any of the measurements of base-lines or of angles, 

 the length of a base obtained by calculation would be the same 

 as that by direct measurement. The results obtained showed 

 a quite marvellous accuracy. Starting from the base meas- 

 ured on Salisbury Plain, the length of another base on the 

 shore of Lough Foyle in the north of Ireland was calculated 

 through the whole series of triangles connecting them, and 

 this calculated length was found to differ from the measured 

 length by only five inches and a fraction. The distance be- 

 tween these two base-lines is about three hundred and sixty 

 miles. 



These wonderfully accurate measurements and calculations 

 impressed me greatly, and with my practical work at survey- 

 ing and learning the use of that beautiful little instrument, the 

 pocket-sextant, opened my mind to the uses and practical 

 applications of mathematics, of which at school I had been 

 taught nothing whatever, although I had learnt some Euclid 

 and algebra. This glimmer of light made me want to know 

 more, and I obtained some of the cheap elementary books 

 published by the Society for the Diffusion of Useful Knowl- 

 edge. The first I got were on Mechanics and on Optics, 

 and for some years I puzzled over these by myself, trying such 

 simple experiments as I could, and gradually arriving at clear 

 conceptions of the chief laws of elementary mechanics and of 

 optical instruments. I thus laid the foundation for that inter- 

 est in physical science and acquaintance with its general prin- 

 ciples which have remained with me throughout my life. 



It was here, too, that during my solitary rambles I first 

 began to feel the influence of nature and to wish to know 

 more of the various flowers, shrubs, and trees I daily met 

 with, but of which for the most part I did not even know the 

 English names. At that time I hardly realized that there 



