OF THE PROPERTIES OF MATTER. 21 



2. It constantly turns one of its sides to the north and LECT 

 another to the south, when suspended to a thread that ^x~v-v 

 does not twist. 3. It communicates all its properties 

 to a piece of steel when rubbed upon it, without losing 

 any itself. 



According to Dr. Helsham's experiments, the at- 

 traction of the loadstone decreases as the square of 

 the distance increases. Thus, if a loadstone be sus- 

 pended at one end of a balance, and counterpoised 

 by weights at the other end, and a flat piece of iron be 

 placed beneath it, at the distance of four tenths of an 

 inch, the stone will immediately descend and adhere to 

 the iron. But if the stone be again removed to the 

 same distance, and as many grains be put into the 

 scale at the other end as will exactly counterbalance the 

 attraction, then, if the iron be brought twice as near the 

 stone as before, that is, only two tenth parts of an inch 

 from it, there must be four times as many grains put 

 into the scale as before, in order to be a just counter- 

 balance to the attractive force, or to hinder the stone 

 from descending and adhering to the iron. So, if four 

 grains will do in the former case, there must be sixteen 

 in the latter. But from some later experiments, made 

 with the greatest accuracy, it is found that the force of 

 magnetism decreases in a ratio between the reciprocal 

 of the square, and the reciprocal of the cube of the dis- 



If this precaution be observed, the following substances will be found to 

 possess magnetic properties. All the metallic ores, amongst which we 

 particularly enumerate iron, cobalt, zinc, and bismuth. The calca- 

 reous are the least attractable of the earths, whilst the siliceous are the 

 most frequently attracted. Amongst the precious stones possessing this 

 property, we may place the emerald, the ruby, tie tourmaline, and the 

 garnet: the last of which freqnently acquires permanent magnetism, 

 which may be accounted for by reference to the large proportion of iron 

 it contains. It may be proper to add, that Dr. Young found a single 

 grain of iron sufficient to make twenty pounds of another metal percep- 

 tibly magnetic. 



