}94 ADVANCEMENT Olt LEARNING. [dOOK V. 



hand be applied to the upper part of the rod, the hand will 



presently be burnt ; but if the heated end be placed upward 

 and the hand applied below, it will be burnt much slower. 

 But if the whole rod were heated, and one end of it wet with 

 snow or a sponge dipped in cold water, would the cold be 

 !:c»oner propagated downwards than upwards if the sponge 

 were applied below? Again, the rays of the sun are reflected 

 from a white body, but absorbed by a black one. Are 

 shadows also scattered by black and collected by white 

 bodies 1 We see in a dark place, where light comes in only 

 at a small hole, the images of external objects are received 

 upon white jjaper, but not upon black. 



An experiment is compelled where it is urged or produced 

 to the annihilation or destruction of the power, the prey 

 being only caught in the other chases, but killed in this. 

 Thus the loadstone attracts iron, — urge, therefore, the iron, 

 or urge the loadstone, till they attract no longer; for ex- 

 ample, if the loadstone were burnt, or steeped in aquafortis, 

 would it entirely, or only in part, lose its virtue ? So if iron 

 were reduced to a crocus, or made into prepared steel, as 

 they call it, or dissolved in aquafortis, would the loadstone 

 still attract it 1 The magnet draws iron through all known 

 mediums, — gold, silver, glass, &c. Urge the medium, there- 

 fore, and, if possible, find out one that intercepts the virtue. 

 Thus make trial of quicksilver, oil, gums, ignited gold, and 

 such things as have not yet been tried. Again, microscopes 

 have been lately introduced which strangely magnify minute 

 obj-ects ; urge the use of them, either by applying them to 

 objects so small that their power is lost, or so large till it is 

 confounded. Thus, for example, can microscopes clearly dis- 

 cover those things in urine which are not otherwise percep- 

 tible? Can they discover any specks or clouds in gems that 

 are perfectly clear and bright to appearance? Can they 

 magnify the motes of the sun, which Democritus mistook for 

 atoms and the principles of things 1 9 Will they show a 

 mixed powder of vermilion and ceruse in distinct grains of 

 red and white 1 Will they magnify larger objects, — as the 

 face, the eye, &c.,-^as much as they do a gnat or a mite, or 

 represent a piece of fine linen open as a net 1 But we need 



* EpisUea of Hippocrates, or Pliny's Nat ]3istory. 



