114 



tions to these assumptions. Mr. Spencer argues very strongly 

 against both, and arrives at the conclusion that matter 

 acts upon matter through absolutely vacant space (p. 60). 

 And in opposition to it, Dr. C. F. Winslow writes in stronger 

 terms still. He says, — There was probably never a grosser 

 error introduced into physical science than the ethereal theory, 

 and its influence in retarding solid progress .... has been 

 greater than at first appears. '^All opinions upon the 

 conditions of infinite space are the merest hypotheses ; and in 

 the midst of conjectures, that would be the most probably 

 correct which presumed space to be a perfect vacuum.^^"^ 



30. The fact that a mna of Dr. TyndalFs very high character 

 and culture can permit himself to affirm so positively what are 

 merely shadowy conjectures, should teach all to weigh very 

 accurately every scientific hypothesis, and would amply justify 

 us in saying that we are not called upon to discuss the per- 

 sistence of energy, while so important an element in the 

 discussion is so confused and undecided. Prove a universal 

 plenum, and even then the continuity of motion is only 

 rendered possible ; but till that is done, we are warranted in 

 asserting its impossibility, and that this grand discovery of the 

 nineteenth century is not a discovery at all, or even a fact. 



31. It may be objected by some that the decrease in the 

 periodic time of Encke^s comet almost demonstrates the existence 

 of such an ethereal medium. Undoubtedly the decrease of the 

 time is a fact ; but the explanation was only a suggestion by 

 Encke, who was not aware of any other force that could act in 

 the interplanetary spaces. M. Eaye has, however, shown that 

 this hypothesis is, if not wholly untenable, at least very im- 

 probable. He attributes the decrease to solar repulsion ; and 

 we think he proves his point very satisfactorily. It is not neces- 

 sary to give here all the steps of his reasoning ; it will suffice to 

 state the general conclusions at which he arrives, showing, as 

 they do, that even Encke's comet does not overturn our former 

 objections to this medium. This theory,^^ he states, "puts in 

 action onlv known forces : the attraction of the sun, — that 

 which the comet exercises on its own particles, the heat of the 

 sun, and the repulsion due to this heat.^^ Again, " My last 

 work had for its object to remove all doubts on this subject 

 in showing that the resisting medium could not exist, but on 

 condition of circulating round the sun according to the laws of 

 Kepler .... and that its action was not constantly resistant, 

 as M. Encke supposed.^^ He also states most truly, That it 



* " Force and Nature," pp. 36, 37, 



