Wire Field Gates. 193 



Postscript in Anstver to some Questions asked of Mr. Sang hy the 



Conductor. 



The instrument for measuring the height of trees is not a 

 pocket sextant, like that of Mr. Blackadder, mentioned in Vol. 

 XIV. p. 257.5 although nearly allied to it. The sextant, qua- 

 drant, reflecting circle, improved Wollaston's goniometer, as well 

 as the optical square and tree-measurer, are all varieties or im- 

 provements on Hadley's first invention. The two latter differ 

 from the rest in the mirrors being permanently fixed at angles 

 suitable for the purposes for which they were intended. The 

 pocket sextant would measure the height of trees quite as well, 

 but, being expensive, and requiring some skill to use it, it is not 

 likdy to be much employed for such purposes. There is no sort 

 of merit in designing the instrument ; and it is so exceedingly 

 simple, that I have no doubt the idea of modifying the sextant, 

 so as to make it readily measure the height of trees, has occurred 

 to many a one. I, however, never heard of such an instrument, 

 and believe that the one you have is the second of its kind in 

 existence. The other is one which was made for yourself. Mv 

 father was so much pleased with it, that he asked me to make 

 one for him, which turned out neater than the first, and accord- 

 ingly I sent it to you, as being the better of the two. As there is 

 nothing like a Greek name for giving identity to it, you might 

 call it a dendrometer, or, better still, a hypsometer (measure of 

 height). 



Of course any instrument-maker could supply these articles; the 

 price, I should think, would be about 205. each. If there were 

 any prospect of selling a dozen or two, I could easily employ a 

 workman here to make them, and they might be sent from the 

 seedshop [see p. 93.] to any place by post. 



Kirkcaldy^ Feb. 10. 1840. 



Art. V. On Wire Field Gates. By George Buist. 



A SINGULARLY light, strong, and unexpensive variety of field 

 and fancy gates has of late been introduced into some of the 

 midland counties of Scotland. They are the contrivance of Mr. 

 George Buist, late of Fifeshire, now of Bombay. They are 

 made wholly of iron, the frame being of light bars, the filling 

 up of wire or small rods. The principle on which they are 

 constructed is, that all the portions requisite for filling up the 

 gate, and which generally only add to its weight and cumbrous- 

 ness, shall be made to act as stays or strengtheners to brace up 

 the frame ; and that these, being all exposed to a longitudinal 

 strain alone, shall be made of very small iron rods, or strong 

 wires, which, when exposed to nearly the direction of their 



