Mr. Sturgeon on an Anomaly in Electro-Magnetism. 47 



produce: but however this may be, they certainly appear to 

 have always confounded such insects with the more common 

 Tabani ; for it is the modern Tabanus, or some genus ex- 

 tremely near to it, that they have always described as the 



I shall take this opportunity of quoting a passage from 

 Mouffet, which proves that he was acquainted with the mo- 

 dern genus CEstrus, although he did not confound it with the 

 ancient ola-rpoi. The passage will also show us how valuable 

 is the information sometimes to be procured from this obso- 

 lete work ; since, if we connect it with what Reaumur has 

 said of the CEstrus eqiii, we have almost the whole economy of 

 this interesting insect : 



" His proxime accedit alia musca bobus et jumentis interdiu 

 sole fervido infesta, quam Pennius Ciirvicaudam sive o-xoXioogoi/ 

 jure appellat. Semper enim cruribus aut ventri jumenti insi- 

 dens, caudam versus ipsam recurvam tenet et spiculurn exer- 

 tum quo ad percutiendum Cauda sit paratior (SiVregov ottktQo- 

 Kv/rpov). Hanc Angli a IV/iame a7id a Bunell-^T/e proprie vo- 

 cant, nee nisi in Anglia facile invenitur. Musca ha^c api fere 

 similis forma et colore, sed corpore est crassiore. Non ad- 

 haeret nee sanguinem sugit sed solummodo stimulo in cauda 

 pungit, atque ut equos affligat per longissima itinera ipsos vo- 

 lando persequitur. Equi natura hanc muscam timent et ad 

 ejus solum contactuni quasi horrent, cauda pedibusque et la- 

 biis tarn cruentum hostem abigere saepe conantes. Sunt qui 

 putant hanc muscam non aculeo pungere, sed stercora [ova] 

 pilis equi affigere cauda, unde postea molestissimae lendes gig- 

 nuntur. Magno quidem impetu sed caeco ad praedam Taba- 

 nus atque ^xoXjoygoj feruntur." p. 62. 



IX. On a supposed Anomaly in the Rotation produced by the 

 Galvanic Current. By Mr. W. Sturgeon. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IT appears to have been hitherto remarked bj^ every writer 

 on Electro-magnetism, that the direction of rotation is al- 

 ways reversed by changing the direction of the Galvanic cur- 

 rent, provided the magnetic bar remains unmolested. It has 

 so happened, however, in one of my experiments, whilst ro- 

 tating a galvanic wire round the pole of a magnetic bar, that, 

 although the latter be not altered in its position, yet the Ibrmer 

 will continue to rotate around it in the same direction, what- 

 ever 



