390 Lord Webb Seymour o« a CUnomcter. 



level, except in the size of the graduated arch, while he observed 

 the bearing at the same time by a compass carried separately. Mi\ 

 Jardine of Edinburgh made the important improvement of having 

 the compass mounted upon the radial bar, and placed it between 

 the center and the graduated arch. Soon afterwards I had an in- 

 strument made in imitation of this, but, in order to reduce the radius 

 of the arch, I had the compass fixed at the end of the radial bar. 

 There was a difficulty in applying the base of this instrument to the 

 surface of a rock, so as to place it with precision in the line of great- 

 est depression, and the endeavour to remedy it led me to the idea of 

 the plate. Two other clinometers were successively made for me 

 upon this plan, with such further improvements as experience 

 gave rise to ; and the last was adapted for observation upon an 

 under surface, upon the suggestion of Mr. Jardine. This laat 

 contained all the principles of the instrument in its present state, 

 and was given as a model to Mr. Troughton, who, in making that 

 which has now been described, introduced a more simple con- 

 struction of the radial bar, and shewed that ingenuity which dis- 

 tinguishes every object of his labours, by other alterations con- 

 ducive to strength and lightness as well as to greater ease and ac- 

 curacy of observation. 



The chief objection to the instrument in its present form, is 

 the weight of the plate. But it is necessary that it should have a 

 certain diameter, in order to admit of its adjustment by the eye to 

 the mean plane of the stratification, and it must have a thickness 

 sufficient to prevent it from bending much under the pressure re- 

 quired to hold it against a steep surface. No substance occurred 

 besides a metal, that was not liable to some objection, particularly 

 that of warping. 



The clinometer may be employed for other purposes, besides 



