48 “dk W. Mallet on Brewsterite. 
But it isa still more serious mistake to say to students, that 
an instrument which performs under a variety of circumstances 
‘without much sensible deterioration” is practically the best for 
all ordinary purposes 
So thought Ehrenberg, and yet we all now know what curious 
mistakes he made. Embryology, too, comes under this pro- 
scription; for any one who has attempted to trace the develop- 
ment of animals, especially the lower forms of life, must know 
that it is impossible to separate the andy, of their cellular struc- 
». ture from the investigation of their or 
cannot more fittingly conclude this communication, than by 
quoting, by Mr. Spencer's leave, a portion of a recent letter of 
his to me. He says: “It seems to me that there is mae. reason 
to nase much from the earnest seth of high powers with 
blin : 
path before them. Every day’s thought convinces me more an 
more deeply of the radical mistake that has been made in this 
tion. y have recently been making some observations and 
’ riments with low angles on certain well-known structures, 
have in several instances been struck with a blank astonish- 
subjects of your study, are precisely such as will lead to the 
most frequent errors; and if you do not find that many a 
blunder has been made in their study, heretofore, I shall be 
greatly surprised.” | 
Art. V.—On Brewsterite; by J. W. MALuer. 
Two analyses of the mineral species Brewsterite are on record, 
a of Vaso — Thomson,t both made many years ago. 
e results 
ell. Thomson. 
Silica, - - : - - 63-666 53°045 
Alumina, - : . : 17-492 16°540 
Baryta, - - - - 6-749 6°050 
St - - - 8°325 “00. 
Lime, - - - - 1°346 
Water, - - 12°584 14°735 
Peroxyd of iron, i : < ee 
100°454 100°175 
* Edinb. N. Phil. Jour. No. XIX, 
+ Outlines of Mineral, Geol ci to Alvi p48 
