4 8. P. Langley — The History of a Doctrine. 



contain illustrations (like that of the hammer driving the nail, 

 which grows hot in proportion as its bodily motion is arrested) 

 ■which show a singularly complete apprehension of views we 



if we consider the nature of it, which seems to consist mainly, if not only, in that 

 mechanical affection of matter we call local motion mechanically modified, which 

 modification, as far as I have observed, is made up of three conditions." 



" The first of these is, that the agitation of the parts be vehement. Thus, in a 



heated iron, the vehement agitation of the parts may be easily inferred from the 



motion and hissing noise it imparts to drops of water, or spittle, that fall upon it. 



• For it makes them hiss and boil, and quickly forces their particles to quit the 



form of a liquor, and fly into the air in the form of steams." 



" The second is this, that the determinations be very various, some particles 

 moving towards the right, some to the left hand, some directly upwards, some 

 downwards, and some obliquely, etc. As a thoroughly ignited coal will appear 

 every way red, and will melt wax, and kindle brimstone, whether the body be 

 applied to the upper or to the lower, or to any other part of the burning coal. 

 And congruously to this notion, though air and water be moved never so vehe- 

 mently as in high winds and cataracts ; yet we are not to expect that they should 

 be manifestly hot, because the vehemency belongs to the progressive motion of 

 the whole body." 



"There is yet a third condition; namely, that the agitated particles, or at least 

 the greatest number of them, be so minute, , as to be singly insensible. For 

 though a heap of sand, or dust itself, were vehemently and confusedly agitated by 

 a whirlwind, the bulk of the grains or corpuscles would keep their agitation from 

 being properly heat. If some attention be employed in considering the formerly 

 proposed notion of the nature of heat, it may not be difficult to discern that the 

 mechanical production of it may be divers ways affected. For by whatever ways 

 the insensible parts of a body are put into a very confused and vehement agita- 

 tion, by the same ways heat may be introduced into that body ; agreeably to 

 which doctrine, as there are several agents and operations by which this calorific 

 motion (if T may so call it) may be excited, so there may be several ways of 

 mechanically producing heat." 



Boyle goes on to cite numerous experiments. 



" Experiment VI. When, for example, a smith does hastily hammer a nail or 

 such like piece of iron, the hammered metal will grow exceeding hot and yet 

 there appears not anything to make it so, save the forcible motion of the ham- 

 mer, which impresses a vehement and variously determined agitation of the small 

 parts of the iron ; which being a cold body before, by that superinduced commotion 

 of its small parts becomes in divers senses hot. Again, if a somewhat large nail 

 be driven by a hammer- into a plank, or piece of wood, it will receive divers 

 strokes on the head before it grow hot ; but when it is driven to the head, so 

 that it can go no further, a few strokes will suffice to give it a considerable heat; 

 for whilst, at every blow of the hammer, the nail enters further and further into 

 the wood, the motion that is produced is chiefly progressive, and is of the whole 

 nail tending one way ; whereas, when that motion is stopped, then the impulse 

 given by the stroke, being unable either to drive the nail further on, or to 

 destroy its entireness, must be spent in making a various vehement and intestine 

 commotion of the parts among themselves, and in such an one we formerly 

 observed the nature of heat to consist." 



" Experiment VII. That I might also show that not only a sensible, but an 

 intense degree of heat, may be produced in a piece of cold iron by local motion, I 

 caused a bar of that metal to be nimbly hammered by two or three lusty men and 

 these soon brought it to that degree of heat, that not only was it a great deal too 

 hot to be safely touched, but probably would have kindled gun-powder." 



Boyle goes on in the eighth experiment to illustrate the production of heat by 

 friction by the use of a file, the whetting of a blade of a knife, the head of a 

 piece of brass rubbed on the floor until it burns one's fingers, the heat of the axle- 

 tree of a carriage by the friction of the wheel, and the common experiment of 

 striking fire with a steel and flint, the latter as illustrating the instantaneity of 

 the production of the heat. 



