Intelligence and Miscellaneous Articles. 315 



racters of anterior sinus and gape ; and, besides E. Scouleri, at least 

 two species have been determined. A very closely related genus, 

 Offa, has also been indicated. M'Coy's " Daphnia primceva " be- 

 longs to Cypridina proper ; and twelve other Carboniferous species 

 have been established. A modified form of carapace, without any 

 exact modern analogue, characterizes the new genus Cypridinella, 

 with seven species. De Koninck's genus Cypridella (restricted) has 

 seven species ; and a form intermediate to this and Cypridina is 

 described as Cypridellina, with eight species. Sulcuna (with two 

 species) is an exaggerated modification of Cypridella. Cyprella of 

 De Koninck (restricted) has two species. The recent Brady cinetus, 

 Sars, and Philomedes, Lilljeborg, appear to have their prototypes in 

 the Carboniferous Limestone, with one species each. Rhombina, 

 a new genus, is a less easily recognized Cypridinal form, with an 

 Irish and a Belgian species. 



The recent Polycope, Sars, belonging to a different family, and 

 represented by three Carboniferous species, was the last described in 

 the memoir ; but Oytherella, belonging to an allied group, is known 

 in the Mountain-limestone and Coal-measures; and Leperditia, 

 Entomis, Beyrichia, Kirkbya, and other palaeozoic genera, abound, 

 together with forms referable probably to Cythere, Cypris, Candona, 

 &c, which will be treated of in a future paper. 



XXXVIII. Intelligence and Miscellaneous Articles. 



ON THE PERMANENT MAGNETISM OF STEEL. BY E. BOUTY. 



n^HE phrase " coercive force " has ever expressed only a somewhat 

 vague comparison between the phenomena of the magnetiza- 

 tion of steel and friction. This bringing together of two orders of 

 phenomena so complex is altogether artificial, and absolutely ex- 

 cludes the facts which relate to the temporary magnetization of 

 steel. 



Wiedmann has, more profitably, brought the phenomena in ques- 

 tion into comparison with those which depend on elasticity in solid 

 bodies, especially the phenomena produced by torsion. Although 

 this comparison does not constitute a theory properly so called, it 

 has the advantage of expressing a real physical relation ; for tor- 

 sion modifies the magnetic state of a bar, and modifications of that 

 state can in turn modify the torsion to which the bar has previ- 

 ously been submitted. A great number of facts relative to mag- 

 netization or demagnetization are conveniently interpreted in this 

 system ; but the following phenomena can only with very great 

 difficulty be adapted to it. 



It has long been known that a certain temporary magnetism can 

 be superposed to a permanent magnetism opposite in direction, and 

 that the latter may reappear, sometimes even integrally, after the 

 influence of the external forces has ceased. For example, if a bar 

 of magnetized steel be submitted to the action of a current too 

 feeble to demagnetize it entirely, during the action of the current a 

 diminution of the magnetism of the bar is observed, which may go 



