212 Don Bustamente on a new Gravimeter. 



15. But if, instead of the second immersion reaching zero, 

 it should remain six divisions below this point, supposing that 

 the scale should have negative divisions, that is, that it should 

 continue below zero, this would show us that the volume of 

 water dislodged weighs more than the substance, because it 

 not only loses from 24 of its weight, but besides, makes the 

 instrument lose six, with which it forms a whole, and the dif- 

 ference between + 24, which it weighs in air, and — 6 in water, 

 observing the rules of the signs, is + 30, dividing 24 by 30, 

 we get 0.8, that is, the specific gravity of the substance is less 

 than that of water. 



16. We have not put on the scales negative divisions, be- 

 cause it would increase much the neck of the instrument, and, 

 besides other inconveniences, would render it more bulky. 

 There is no necessity for these divisions, if we consider, that, 

 by increasing the additional weight, we can sink the greater 

 part of the scale, in order that the substance that we might 

 weigh in water should afterwards make it rise, and by this 

 simple proceeding we can say, that, without altering the size 

 of our scale, we have doubled it. An example will illustrate 

 this. 



1 7. Suppose a small piece of oak weighs in air 43.3, taking 

 it from the upper plate, and increasing the additional weight? 

 we shall make the scale sink to 60 for example. Marking this 

 point, which we shall consider as though it were the zero of 

 the scale, and weighing afterwards the wood in water, the im- 

 mersion only reaches to 53, that is, it has seven divisions, which 

 certainly correspond below zero. The difference, then, be- 

 tween -f- 43.3, weight of the oak in air, and — 7.0, its weight in 

 water, is -f- 50.3. Dividing 43.3 by 50.3, the quotient, 0.860, 

 results, which is the specific gravity of oak ; and this operation 

 will be observed in other instances. 



18. If, when the instrument is at zero, we place known 

 weights, such as drachms and grains, we shall know the cor- 

 responding weight of each division of those that are immersed, 

 dividing the number of drachms or grains by the number of 

 divisions; so then, if with 3 drachms or 108 grains it sinks 54 

 divisions, each one will correspond to 2 grains, and in this 

 manner we shall know how far the greatest weight that can 

 be weighed in this instrument ascends. 



