& 157 
cluded within the mother-cell, while the tails have become 
disengaged and vibrate freely in the external fluid. 
In the mother-cells, besides the spermatozoa in their vesi- 
cles of evolution, a large, well-defined, nucleus-like body, with 
considerable refractive powers, seems to be invariably pre- 
_ sent. 
The motions of the free spermatozoa are peculiar, and con- 
sist in a succession of sudden jerks. 
By permission of the Academy, Mr. T. A. Dillon ex- 
plained a plan of his for ascertaining the deviation of ships’ 
compasses arising from local attraction. 
<¢ Str,—I have the honour to submit, for the consideration 
of the Royal Irish Academy, a plan which I hope will tend. 
_ in some degree towards reassuring the proprietors and com-- 
_ manders of iron ships, whose uneasiness in consequence of Dr. 
Scoresby’s communication, ‘ On the Influence of Iron Ships 
over their own Compasses,’ has been, and still continues to be, 
of the most serious character. 
*¢ What Dr. Scoresby says is this:—<‘ So soon as a vessel 
_ made of iron puts to sea and undergoes the tossing and strain- 
ing of the waters, she becomes an immense magnet, as it were, 
_ something in the same way that a poker is transformed into a 
magnet by striking it repeatedly with a hammer.’ And this 
distinguished philosopher goes on to state, that the loss of the 
Tayleur, and of many other iron vessels, can be assigned to-no 
other cause than to the very startling one above mentioned ; 
for the proximity of such an enormous magnet to the delicate 
compass needles disturbs and overrules these instruments as a 
matter of course. The ship goes astray, and all hands perish. 
““Now, it little matters whether Professor Scoresby’s magne- 
tic theory be correct in every particular or not. We know that 
" the most admirably constructed instruments have mysteriously 
4 gone wrong, even after every scientific precaution had been 
i taken to preserve and compensate them in the most perfect 
- VOL. VI. P 
q 
