NOVUM ORGAN UM. 167 



vapour or air in the water, but is chiefly created by the 

 expansion of the water by the heat of the fire. 



So in general all delicate experiments on natural or arti 

 ficial bodies, by which the genuine are distinguished from 

 the adulterated, and the better from the more common, 

 should be referred to this division; for they bring that 

 which is not the object of the senses within their sphere. 

 They are therefore to be everywhere diligently sought after. 



With regard to the fifth cause of objects escaping our 

 senses, it is clear that the action of the sense takes place 

 by motion, and this motion is time. If, therefore, the 

 motion of any body be either so slow, or so swift, as not to 

 be proportioned to the necessary momentum which operates 

 on the senses, the object is not perceived at all; as in the 

 motion of the hour hand, and that again of a musket ball. 

 The motion which is imperceptible by the senses from its 

 slowness, is readily and usually rendered sensible by the 

 accumulation of motion ; that which is imperceptible from 

 its velocity, has not as yet been well measured ; it is neces 

 sary, however, that this should be done in some cases, with 

 a view to a proper investigation of nature. 



The sixth case, where the sense is impeded by the power 

 of the object, admits of a reduction to the sensible sphere, 

 either by removing the object to a greater distance, or by 

 deadening its effects by the interposition of a medium, 

 which may weaken and not destroy the object; or by the 

 admission of its reflection where the direct impression is too 

 strong, as that of the sun in a basin of water. 



The seventh case, where the senses are so overcharged 

 with the object as to leave no further room, scarcely occurs 

 except in the smell or taste, and is not of much consequence 

 as regards our present subject. Let what we haye said 

 therefore suffice with regard to the reduction to the sensible 

 sphere of objects not naturally within .its compass. 



Sometimes, however, this reduction is not extended to 

 the senses of man, but to those of some other animal, whose 

 senses, in some points, exceed those of man : as (with regard 

 to some scents) to that of the dog, and with regard to light 

 existing imperceptibly in the air, when not illumined from 

 any extraneous source, to the sense of the cat, the owl, 

 and other animals which see by night. For Telesius has 

 well observed that there appears to be an original portion of 

 light even in the air itself, although but slight and meagre, 

 and of no use for the most part to the eyes of men, and 

 those of the generality of animals ; because those animals 



