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Prof. NECKER on the Determination of the 



given by all those who have the opportunity of making geologi- 

 cal observations in any part of the world, has induced me to con- 

 trive a very simple mechanical apparatus, by which all such prob- 

 lems could be easily, and in a very short time, solved. It is this 

 instrument which I call the Clinometrical Compass, of which I 

 am now to give the description, at the same time that I have 

 the honour to lay it before the Royal Society. 



This instrument is composed of a circular plate of brass A B, 

 divided in thirty-two parts, corresponding to as many points of 

 the compass. A semicircular plate of brass 1C, concentric to the 

 above mentioned circle, is made to turn upon it around the com- 

 mon centre. This semicircle is also divided by lines in sixteen di- 

 visions, exactly corresponding to those of the under circle. A 

 semicircular portion of a ring of brass E, concentric with both 

 plates, is connected by a hinge F, with the diameter of the semi- 

 circular plate, in such a way that the diameter of this plate and 

 that of the half ring are made to coincide in the hinge. In this 

 manner the ring may be moved upwards or downwards, so as to 

 take any inclination whatever upon the horizontal plane, or upon 

 the plane of the lower circular plate, by which the horizontal 



.? n .11 TBA'I J1X . lOV 



