On the Resistance of Fluids. 167 



ber of the particles encouiitered in a given time." Now, I ask what 

 is a given instant but a given time ? I will venture to say that Prof. 

 Wallace would not admit that there is any difference between either 

 his method or his result and those of the common theory, when the 

 question relates to the action on planes perpendicular to their line 

 of motion, and moving with different velocities. The difference be- 

 tween Prof. Wallace and the common theory is this : when equal 

 planes are differently inclined to the line of motion, and moving with 

 equal velocity, the common theory says that the number of particles 

 striking the plane in a given time, depends on the inclination of the 

 planes ; Prof. W. says it does not. Prof. W. reasoned rightly from 

 his premises ; but they were wrong ; to show which was the object 

 of my former communication. I ought to remark that all I know of 

 Prof. Wallace's views is from the paper of Mr. Gibbes. 



Mr. B. further asserts that 1 pursue the subject in opposition to the 

 views of Prof. Wallace, only to the point at which he first begins to 

 diverge from the common theory. The truth of this assertion de- 

 pends on that of the preceding, which is yet to be proved. 



Mr. Blake, at last, says, we are both wrong, and indeed that all 

 that has been published on this subject is more or less wrong. Let 

 the readers of the Journal decide. I wish to be brief. I have there- 

 fore made the truth of Mr. Blake's first assertion the main point in 

 this discussion. He considers it fundamental ; so do I; if I have 

 proved what I proposed in regard to that, those who are interested 

 will apply it, and they will find that Mr. B.'s error there has vitiated 

 his reasonings. 



It is unnecessary for me to deny or to admit the justness of the dis^ 

 tinctions among forces which is made at the outset by Mr. Blake, 

 since I have shewn that these distinctions are not regarded by him. 



On first reading Mr. B.'s communication, I determined not to 

 comment on it. But it occurred to me that there are many readers 

 of the Journal who are not so well informed in theoretical philosophy, 

 or, so much disposed to do it justice as Mr. Blake, and that his state- 

 ments, if not contradicted, were just such as would promote that 

 hostility of theoretical and practical science, which, I am sure, Mr. 

 Blake himself has done much to destroy. I do not wish to conceal 

 the fact, that the common treatises on Natural Philosophy are very 

 defective, but let us not charge them with defects that do not belong 

 to them; and above all, if the accuracy of the demonstrations and 

 conclusions of such minds as Newton's must be impeached, let it be 

 done, I will not say timidly, but cautiously, and with respect. 



