idmethyst of Ithode Island. 401 



Any gentleman or public institution, wishing to become at 

 once possessed of a large and beautiful collection of minerals 

 on very reasonable terms, may now have an opportunity. 

 The whole will be disposed o( (or Jif teen hundred dollars. 



Persons interested will obtain further information by ad- 

 dressing letters (post paid) to Dr. Morton, Arch St. Phila- 

 delphia where the collection is arranged, and may be seen. 



Philadelphia, June 2, 1825. 



20 Bolles's Trigonometer. We have examined an instru- 

 ment invented by Mr. William Bolles of Griswold, Conn, for 

 the purpose of solving mechanically, questions in plain and 

 spherical trigonometry, and called a trigonometer. The 

 plan of this instrument, and the uses to which it may be ap- 

 plied, may be gathered from the plate, and the description 

 that follows ; but they are more particularly disclosed in a 

 pamphlet published, by the inventor, a copy of which always 

 accompanies the instrument. (See plate IV. fig. 10.) 



A, D, and C, are three rods of metal, graduated to a scale 

 of equal parts. C E is an arc on which the rod D C may 

 be opened to any required angle : A B is a similar arc fixed 

 to the rod A, on which, by means of a centre at a, the rod C 

 can be opened to any angle, a 6 is a metallic piece carrying 

 that centre, and having a groove along which slides the rod 

 C. b b are screws to fix the rods firmly at the required an- 

 gles. It is evident that by means of the arcs, the interior 

 edges of the three rods may form a triangle similar to any- 

 given triangle ; and by means of the sliding part C, may be 

 adjusted to any numerical values within the limits of their 

 graduation. 



How far an instrument like this will ever be applied in 

 practice to the purposes for which it is designed, must depend 

 on the accuracy with which it can be constructed at a mod- 

 erate expense. Unless constructed with more exactness than 

 most of the mathematical instruments that are commonly 

 sold, it would be found of slight value. But if made with 

 care, it is likely that an instrument of this kind will be found 

 valuable by surveyors and seamen in all cases in which ex- 

 pedition is required without much numerical accuracy, 



21. Amethyst of Rhode-Island. — We are informed by a 

 correspondent, that the amethyst mentioned (in a note p. 

 40 of this Vol.) as being cut and set in gold, by Mr. George 



Vol'. IX. No. 2. 51 



