Mr Solly on the Motion of Earthquakes. 183 



The screw H is attached to the part D by means of a re- 

 volving joint, and it works in the nut at C, so that, on being 

 turned, it alters the inclination of the part D to the fixed part 

 A. 



The part I, which contains the outer axis of the theodolite, 

 has an axis (like E) working in the sockets F F. 



The screw K, working in the nut at G, and being attached 

 to the part I by a revolving joint, alters the inclination of I 

 with regard to D ; so that, by means of the two screws H and 

 K, the part I can be inclined in any manner to the fixed part 

 A, while there is in every portion of the apparatus a firm re- 

 sistance to a motion in azimuth. 



The small screw L is intended to temper the pressure of a 

 piece of tin, inserted into the nut to make up for the wearing 

 of the levelling screw. 



This apparatus will add to the expense of a theodolite, but 

 by no means in proportion to the time which it will save. 



John Sang. 



KiBKCALDT, ^th Nov, 1843. 



Observations on the Motion of Earthquakes transmitted under 

 the Andes. By RiCHARD SoLLY, Esq. Communicated by 

 the Author. 



Sir, — Having been lately engaged on a paper for the Shef- 

 field Literary and Philosophical Society, the subject of which 

 was earthquakes, I have been much interested in the valuable 

 communications published in your Journal, especially those of 

 Professor Bischof, Dr Daubeny and Mr Milne. One or two 

 remarks have occurred to me respecting a fact which I have 

 not seen alluded to by any of our geologists, but which you 

 may perhaps consider as not altogether unworthy of their at- 

 tention. I refer to the shocks of earthquakes having extend- 

 ed beyond vast mountain ranges, and yet having been felt 

 either very slightly, or not at all, in those mountains. 



Mrs Maria Graham, in her account of the great earthquake 

 of the 19th November 1822,* which destroyed so many build- 



* Trans, Geol. Soc. 2d series, vol. i. part ii. p. 413. 



