The Eighteenth Century 173 



before, to a lesser and lesser degree, and finally almost to a state of rest. 

 Therefore there may be sometimes much fire in a body with but little 

 motion, or with but small effects of it; and sometimes but little fire with 

 a great effect. Perhaps phosphori prepared from the parts of animals are 

 of that nature, that whereas they are cold under water, and not shining, 

 but only shine out of water, they may possibly contain a great deal of 

 fire, but which is chiefly at rest. 



The relation of fire and light to air were discussed as follows: 



Hot water sooner loses it's fire in Boyle's vacuum, than in the open air. 

 Rotten and shining wood, surrounded by air, retains it's fire for some 

 days, of which it will be soon bereaved if put into Boyle's vacuum. This 

 wood, when once deprived of it's fire, does not recover it again by being 

 restored to the air. Lampyris shines in the air, in the vacuum ceases to 

 shine, and admitting the air it shines again. Yet iron keeps it's fire 

 longer in vacuo than in the air; and perhaps many other bodies are 

 subject to the like irregularities. . . . Fire therefore is present every 

 where, and in every body, and that which before was almost at rest, or 

 but little moved, by rubbing being again swiftly agitated from such 

 parts, as by a vibratory motion tremble very briskly, then shews it's 

 presence and efficacy. 



Regarding light, van Musschenbroek wrote: " Light is a most fluid 

 matter, and therefore like other fluids consists of particles not coher- 

 ing with one another," and then asked: 



First, how do light and fire differ? Is it in substance, or only in the 

 magnitude of their parts, or in the direction of their motions? Perhaps 

 not in substance, nor in the magnitude of their parts, since a great quan- 

 tity of light collected together has always the characters of fire. But 

 fire does not shine, unless when determined to the eye in right lines. A 

 silver spoon heated does not shine in the dark; but if you put diamonds 

 or crystals into it, though they did not shine before, yet they soon begin 

 to shine, expelling the fire they had received under the form of light. 

 They do the same thing, if thrown into hot water. . . . 



Lastly, do not those bodies shine most easily, which abound with oily 

 and sulphureous parts, as soon as they begin to move by friction, per- 

 cussion, putrefaction, vital motion, or by any other cause? For what 

 reason does the sea shine, when tossed by the winds? or the back of a 

 cat, the neck of a horse, when rubbed contrary to the natural situation 

 of the hair? or wood, flesh, fish, when rotten? the eyes of animals and 

 glow-worms? Also a glass ball in violent rotation, and rubbed by the 

 hand, why does it emit a blue light sticking to the hand? 



The influence of Newton is marked. It is apparent that van 

 Musschenbroek was familiar with the most diverse luminous phe- 

 nomena and tried, without too great success, to fit this knowledge 

 into a general theory of fire and light. 



