208 Don Bustamente on a nexv Gravimeter. 



cessary to be adding and taking away the weights as may be 

 required, to bring that point exactly level with the surface of 

 the water, which proceeding is tedious. Besides on journeys, 

 where the conveniences one has at home are generally wanting, 

 it is very easy to lose some of such small weights, by which 

 means an instrument so useful to the travelling mineralogist 

 is rendered useless. To avoid these inconveniences, faci- 

 litate the transport of the instrument, and simplify the opera- 

 tion, I make use of the instrument which is represented in 

 Fig. 1, ^, and 3 of Plate II., which gives the necessary instruc- 

 tions for ascertaining the specific weight of minerals with great 

 exactness without weights. 



2. The part a b c oi the instrument, which may be of tin, 

 brass, &c. is composed of two inverted cones, hollow and 

 united at d e^ as Fig. 1 shows, the base of which is a concave 

 plate, afh^ which receives the minerals that are weighed in 

 water. Before soldering this plate, the instrument must be bal- 

 lasted, that is, a portion of lead is put into it so as to sink it 

 in the water till near the base a 6.* 



3. In four points of this base, opposed at right angles, are 

 soldered two arches of wire a b, g h^ which cross, and sustain 

 the hoop m, which receives the end of a crystal tube m n, made 

 fast with sealing wax. In the interior of the tube is placed a 

 scale of lines, of millimetres or of equal arbitrary parts traced 

 on paper, and the divisions of which are numbered from zero 

 upwards.*!* 



4. Finally, on the other end of the tube is fixed, by means of 

 a hoop and sealing wax, the plate r s, which is used for putting 

 the minerals into when they are required to be weighed in air. 



5. Figure 2 is a' cylindrical box of tin with its cover, of the 



* The ballast may be of lead, in flat pieces, or small shot. In the first 

 instance, it is well fitted, and stuck to the sides of the inferior cone ; but 

 in the other two it will be necessary to fix it with a cover of tin soldered 

 to the cone, so that they do not shake about, and are always kept at the 

 bottom. 



t Instead of a glass tube, one of silver or brass might be used of the 

 corresponding size and weight. On the outside let there be a scale of 

 equal parts ; then suppress the hoops ; and the arches, as well as the plate, 

 will be better fixed to the tube, and the instrument less exposed to get 

 damaged. 



