tal 
| “Amethyst of Rhode 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 of for fifteen 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. 
fig. 10.) 
, D, and C, are three rods of metal, graduated to a scale 
of equal parts. is an arc on which the re may 
be opened to any required angle : A Bis a similar are fixed 
to the rod A, on which, by means of a centre at a, the rod C 
can be opened to any angle. a6 is a metallic piece carrying 
that centre, and having a groove along which slides the rod 
C. 6 bare screws to fix the rods firmly at the requiredfan- 
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 yalues within the limits of their 
graduation. | 
How far an instrument like this will ever be applied im 
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 
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 ye 
40 of this Vol.) as being ¢ut and set in gold, by Mr. George 
Vor. IX. No. 2, 51 
