lever about three inches long may project from its centre: this is to be held in the hand, the thumb and index finger operating on the rackwork, while the two little fingers give a rotatory motion by working the lever end. _This rapid double motion is here completely under the command of_ one hand, _while the other is at liberty to adjust the focus_. I know of nothing better for general purposes, or in particular for following the motions of live insects, &c.; but when _only inanimate ones_ are to be the subject of microscopical study, I prefer the motion of the stage, for the reasons stated by Mons. C. _On the Existence of Chlorine in the Native Black Oxide of Manganese._ By John M’Mullen, Esq. In the paper relating to this subject, which the editors of the Quarterly Journal of Science obligingly inserted in the forty-fourth number of that work, I described some experiments which I had made, to show that chlorine is uniformly evolved from the Native Black Oxide of Manganese by the action of sulphuric acid, under certain circumstances, which I endeavoured to detail with strict accuracy, so as to prevent any mistake or failure in the event of the experiment being repeated. Upon this paper Mr. Richard Phillips has made some observations in the Philosophical Magazine and Annals of Philosophy for April last, to which I am desirous of briefly adverting. He says, “Mr. M’Mullen having observed, when sulphuric acid is added to peroxide of manganese, that chlorine is evolved, he conceived it might be derived from an admixture of muriate of manganese, iron, or copper; but having washed some of the peroxide of manganese with water, he did not find that any chloride of silver was precipitable from it; he, therefore, concluded that the peroxide in question contained no muriatic salt.” If Mr. Phillips will take the trouble to refer to my paper, he will find that this is by no means the statement which it contains. I observed that, in order to separate any soluble [p259] muriates which the oxide used might, in the first instance, have contained, “I washed it every day, for three weeks successively, using sometimes hot and sometimes cold water: _at the end of that time_, I tested the water, which was _then_ decanted from the washed manganese, by the nitrate of silver, but without finding the slightest appearance of precipitated chloride. I then poured upon the manganese four times its weight of dilute sulphuric acid; allowed the mixture to stand _for about four weeks_, occasionally agitating it, and at the end of that time, found, when the dilute acid, now of a deep crimson colour, _was removed from the subsident manganese_, and the latter agitated, that the most decisive evidence of the presence of chlorine was exhibited in the vapour evolved from it.” I stated further, that I had “carefully preserved this particular mixture, and that after a lapse of more than twelve months, the residuary