286 Mr. W. Phillips's Hints to an Edinburgh Reviewer. [April, 



rately ; but really I am compelled, though with regret, to con- 

 clude, that the Reviewer in question must be deficient in all 

 these requisites, and he must excuse me if I proceed to the 

 proof. 



Supposing that the " author of the work before us," as the 

 Reviewer has it, had not known better than to assert that the 

 " cleavage planes of different individuals of the same species 

 meet in some cases under angles of different values ; " the 

 Reviewer ought himself to have known enough of the subject to 

 have enabled him to contradict the assertion, and to set the 

 author and his own readers right, instead of building upon so 

 unfounded a position, as the Reviewer has done, a sort of battery 

 against " crystallographical indications;" which, indeed, as the 

 case stands, is a very harmless one. But the Reviewer could 

 not have been aware of the fact, that the planes of cleavage of 

 different individuals of the same species do always meet at the 

 same angles, if the cleavages and the selection of the minerals 

 be made with proper care ; and I cannot refrain from advising 

 him to convince himself of this fact, by beginning with calca- 

 reous spar, sulphate of barytes, or any other of the several mine- 

 rals which are commonly chosen for the first attempts of the tyro 

 in this important and interesting department of the science. 

 Let him give only an hour or two to cleavage and the reflective 

 goniometer, and he will not fail to convince himself that if I 

 had said what he attributes to me, I should have mis-stated a 

 fact ; but as he must be unacquainted with that well-known 

 fact, I think it is sufficiently apparent that he must be deficient 

 in the first requisite — a knowledge of the subject ; that is, of 

 mineralogy. 



The existence of the second and third requisites maybe discuss- 

 ed together. The place in which I have mentioned an occasional 

 variation of 40 minutes in angles obtained by the reflective gonio- 

 meter, and I believe the only place, is in the second page of the 

 advertisement to the third edition. Now if the Reviewer had 

 given a reasonable attention to the former part of the paragraph 

 in which that observation occurs, he would have found out that 

 I was speaking of the natural planes, not the cleavage planes of 

 crystals. My words are, " the measurements of the crystalline 

 forms, and especially of the secondary planes, are not precisely 

 exact, do not on all occasions relatively agree. — It has been 

 ascertained by a comparison of the measurements taken from 

 similar and brilliant planes oj different crystals," [the planes of 

 crystals can be no other than their natural planes] " that, owing 

 to some natural inequality of surface, the same precise angle is 

 rarely obtained — that the limit of error is considerably within 

 one degree — that it rarely exceeds 40 minutes, and that it is 

 frequently confined to a minute or two." And if the Reviewer 

 had read a few more lines of the same paragraph, he would have 

 been convinced, even if the above quoted words had not served, 



