Philosophical Transactions. 129 
dering the variations of the magnetic needles more sensible, and he 
commenced a series of observations in consequence of the commu- 
nication. — : 
He ascertained, that there was an easterly deviation before eight 
o’clock in the morning, and that the greatest westerly deviation 
took place about one o’clock in the afternoon. He also found, 
that the state of the weather had a considerable influence upon 
the nature and extent of the changes. But the most striking effects 
seemed to him to arise from changes of temperature, and he adopts 
the opinion that temperature, if not the only cause of the daily 
variation, is the principal. He expresses his intention of entering 
fully into the general question, when he shall have ascertained the 
precise effects of changes in the temperature of magnets. 
13. On Fossil Shells. By Lewis Weston Dillwyn, Esq., F.R.S. 
[In a Letter addressed to Sir H. Davy, Bart., P.R.S.] 
Mr. Dillwyn remarks, that every turbinated univalve of the older 
beds, from transition lime to the lias, of which he can find any re- 
cord, belongs to the herbivorous genera, and that the family has 
been handed down through all the successive strata, and still in- 
habits our land and waters. On the other hand, all the carnivo- 
ruos genera abound in the strata above the chalk, but are compa- 
ratively extremely rare in the secondary strata, and not a single 
shell has been detected in any lower bed than the lower oolite. 
‘He thinks, that a further examination will prove, that neither the 
aporrhaides or any of those few undoubtedly carnivorous species, 
which have been found in the secondary formations, were furnished. 
with predaceous powers, but that they belong to a subdivision of 
the trachelipoda zoophaga, which feed only on dead animals. 
14. On the apparent Magnetism of Metallic Titanium. By William 
: Hyde Wollaston, M.D., V.P.R.S. 
In this paper Dr. Wollaston corrects an oversight in his former 
communication upon metallic titanium. He therein stated, that 
_ when the crystals from the slag had been freed from all particles 
of iron adherent to them, they appeared to be no longer acted upon 
‘by the magnet. He has since found, that although they are not 
‘sufficiently attractive to be wholly supported by the magnet, yet, 
‘when a crystal is supported by a thread, the force of attraction is 
sufficient to draw it twenty degrees from the perpendicular. From 
‘an ingenious comparison of different magnetic forces, he calculates 
“that 51, part of iron, as an alloy in the metallic titanium, would 
‘be sufficient to account for this power; and he shews, that it is 
‘extremely difficult chemically to detect so minute a portion of iron, 
on account of the high colour of the precipitates of titanium, 
Vor. - XVII, K 
