Geographical and Topographical Improvements. £!5l 



tt meets with resistance at the point G, it gradually forces 

 back the cross piece I, by means ot" the female screw within 

 it, and compresses the spiral into a small space, between 

 the two cross pieces, in which state it reniains, till the 

 article which is pressed in the box begins to give out a part 

 of its contents. The spiral spring M, compressed as above 

 mentioned, then begins to expand, and exerts a continued 

 re-action upon the cross piece I, on the male screw H, 

 the iron plate of which covers the article under pressure. 



Fig. 3, is the male screw, separated from the other parts, 

 to show how f;.r the thread or worm extends upon it. 



XLVI. Geographical and Topographical Improvements pro- 

 posed by John Churchman, Esq. ]\lemher of the Im- 

 perial Academy of Sciences at St. Petershurgh *', 



T ^^^'' 



X. REauESTyou to lay the following cssav on the improvci- 



ment of geography before the Society for the Encourage- 

 ment of Arts J and, in so doing, 3'ou will much oblige 

 Your most obedient servant, 



John Churchman. 

 Charles Taylor, Esq. 



It appears to be a matter of much iniportance to the 

 people of any country, at all times, whether in war or 

 peace, to possess a complete knowledge of its surface. In 

 war, such knowledge is absolutely necessary for defence ; 

 in peace, for improving the country to the best advantage. 



is'ow, since geography may be improved, an easy and 

 accurate method to lay down maps of mountainous coun- 

 tries and hilly estates will perhaps prove uscfid, as it will 

 show at a single view the true shape and comparative height 

 of the ground without the art of pamting. 



As moiuuains are apt to eclipse each other, a pcrsptcl.ve 

 view is seldom very extensive, the rules ol which iali short 

 of giving an accurate idea of any hilly country; because 

 such a view, though strictly true in one particular place^ 

 is not so in any other. The altitudes of mountains appear 

 in ))roportion to the distance from the eye, and no rule in 

 geometry has been ibund .sufli<'ient to determine distances 

 from any single station. Neither can a biid's-eyc view of 

 an estate ascertain the depth of vallevs or the height of 

 jnountains. iJut the method here proposed will be found 



• From l.ansacttons of the S/tuty <J Aris, &c. vol. xxii. 



1 equally 



