136 HISTORY OF SCIENCE. 



which may continually be present or absent, and always increase and 

 decrease with that nature." The first work in the discovery of forms 

 is to throw out or exclude such particular natures as are not found in 

 any instance, or such as are in any instance found where that nature 

 is absent ; or again, such as are not found to increase or decrease with 

 the given nature; "and then, after this rejection or exclusion is duly 

 made, the affirmative, solid, true, and well-defined form will remain 

 as the result of the operation, while the volatile opinions go off, as it 

 were, in fume." This exclusion contracts the field of inquiry, and 

 brings the true explanation of the case more within reach. Thus, sup- 

 pose the subject in question be the "form of transparency," or that 

 quality which is the cause of transparency in bodies : now, since the 

 diamond is transparent, we immediately exclude fluidity and also/0- 

 rosity, because the diamond is a solid and a dense substance. In a 

 fourth table Bacon accordingly proposes to exhibit an example of this 

 exclusion or rejection of natures from the form of heat. Thus, as both 

 the sun's rays and a common fire are hot, he excludes both " the ter- 

 restrial and the celestial natures " as causes of heat. Luminosity is 

 also excluded, because the rays of the moon and stars present light 

 without sensible heat. Tenuity as a cause is rejected, because a dense 

 substance like gold can readily be made hot, while air as a thin and 

 subtile substance is generally cool. Other things there are which may 

 also be excluded ; but Bacon does not design these tables to be perfect, 

 but to be merely examples. He adds that " the business of exclusion 

 lays the foundation for a genuine induction, which, however, is not 

 perfected till it terminates in the affirmative; for a negative conclusion 

 cannot possibly be perfect. By the guidance of these tables, however, 

 affirmative conclusions may be provisionally put forward, subject .to 

 subsequent revision and verification." These affirmative conclusions 

 occupy \hefifth table, which Bacon quaintly styles "T/ie First Vintage 

 concerning the Form of Heat" and he thus concludes it and his example 

 of an investigation : " Let this serve for what we call the first vintage, 

 or an attempt towards interpreting the form of heat which the under- 

 standing makes, as we said, by way of permission. The fruit of the 

 first vintage is, in short : Heat is an expansive bridled motion, strug- 

 gling in the small particles of bodies. But this expansion is modified, 

 so that, while it spreads in circumference, it has a greater tendency 

 upwards. It is also vigorous and active ; and as to practice, if in any 

 natural body a motion can be excited which shall dilate or expand, 

 and again recoil or turn back upon itself, so that the dilation shall not 

 proceed equally, but partly prevail and partly be checked, any man 

 may doubtless produce heat ; and this may serve as an example of 

 our method of investigating Forms." 



It is interesting to observe that Bacon's guess as to the cause or form 

 of heat being motion of the small particles of bodies, has, in modern 

 times, received an ample verification ; for the dynamical theory of heat 



