conductivity has been found to be the same as that of their electrical conductivity.
As regards the magnetic permeability of these alloys, the order is very different from that of their electric conductivity. The most highly permeable alloys are those formed of aluminium and silicon with iron. In fact, the magnetic permeability of an alloy of iron with 2\ per cent, of silicon exceeds that of the best and purest annealed iron up to a field of 10 C.G.S. units. Still more remarkable is a pure and well annealed alloy of aluminium and iron ; although it contains a con- siderable percentage of non-magnetic elements, its magnetic perme- ability and maximum induction up to a field of 60 units exceeds the best and purest annealed iron that I can obtain, a specimen of Swedish charcoal iron containing 99*9 per cent, of iron, all the specimens having been subjected to a precisely similar annealing process.
It is possible the increased magnetic susceptibility given to iron by aluminium, and to a less extent by silicon, may be due to the strong chemical affinity which these elements have for oxygen, whereby any of this gas which might be dissociated in the molten iron would be removed, and the texture of the metal thus rendered closer and more uniform. In the same way, by combining with the oxygen, they would remove, as my colleague Professor Hartley suggests, traces of oxide of iron, more or less diffused through all iron ; and the presence of which would certainly lower the magnetic susceptibility.
The remarkable magnetic properties of these two alloys, especially of the aluminium-iron alloy, is a matter not only of considerable theoretic interest but obviously is also of great practical importance in electrical engineering.
" On a Pair of Ciliated Grooves in the Brain of the Aminoccvte apparently serving to promote the Circulation of the Fluid in the Brain-cavity." By AUTHUK DEXDY, D.Sc., F.L.S., Professor of Biology in the Canterbury College, University of New Zealand. Communicated by Professor G. B. HOWES, LL.D., F.PuS. Pteceived February 7, Kead February 20, 1902.
The peculiar and apparently hitherto undescribed structures which form the subject of the present communication, were first discovered in the course of an as yet unfinished investigation of the parietal organs in the New Zealand Lamprey (Geotrui australis). The Ammoca-te of this interesting species is known to us only through two specimens :
