210 GENERAL CONDITIONS OF SCIENTIFIC RESEARCH. 



their complexity ; and many also in consequence of the 

 number of interfering circumstances which cannot be 

 excluded ; the latter is particularly the case in experiments 

 upon living structures. Many are difficult in consequence 

 of extraneous circumstances, such as rarity of the requisite 

 substances or conditions necessary for the experiments or 

 observations ; some through slowness of process, or great 

 length of time required ; some owing to great magnitude 

 or cost ; others in consequence of minuteness of the sub- 

 stances, or feebleness of the actions, the want of powerful 

 and delicate instruments, or tests, &c. 



The difficulties of research arise largely from our 

 ignorance. Many of the phenomena we are acquainted 

 with and which seem rare, are probably only the more 

 conspicuous instances of common effects. A vast number 

 of phenomena continually before us are unnoticed, owing 

 to their excessive smallness of amount, extreme slowness 

 of action, &c. We are as yet acquainted only with the 

 comparatively common and more conspicuous phenomena 

 of matter, the structures and actions of masses ; and are 

 almost entirely unacquainted with the actual sizes, forms, 

 positions, weights, and directions of movement, of the 

 molecules of the substances we use ; and as the phenomena 

 of masses are but collective results of those of the mole- 

 cules, and as those molecules are all of them often pro- 

 foundly disturbed by every change of mechanical force, 

 light, heat, electricity, magnetism, or chemical power, 

 and some of these forces are always acting upon them, 

 it is evident we continually operate in almost complete 

 ignorance of some of the most fundamental conditions of 

 our experiments. 



We occupy, as human beings on this globe, the position 

 of creatures of almost infinitely feeble power, helplessly 

 subject to the influence of an immense number of circum- 



