4 157 
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. 
«¢ Sir,—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 
gone wrong, even after every scientific precaution had been 
taken to preserve and compensate them in the most perfect 
VOL. VI. P 
