We cannot flatter ourselves that we have done more during our three-and-a-half years’ work than contribute a few facts towards the data necessary for the solution of the problem, “What is the cause of the beautiful phenomenon of stratification produced by electric discharges in vacuum tubes ?” which, having been first noticed by M. Abria in 1843, was independently re-observed by Mr. (now Sir William) Grove in 1852, and has since engaged the attention of so many physicists. Our excellent and highly esteemed friend the late Mr. Gassiot, working at first with an induction coil, but more recently on the same lines as ourselves (voltaic batteries of high potential), has published results of great interest, many of which are confirmed by our own experience; while, on the other hand, we have enjoyed pleasurable intercourse and exchange of thought with our contemporary, Mr. W. Spottiswoode, who is still pursuing with great acumen and originality a similar investigation, both with the induction coil and the Holtz machine, with which he has recently used condensers of great capacity, like those we employ and have described in Part I. If we arrive at the same results by different paths, the one investigation will support the other, and for each may be claimed more reliance than if unconfirmed. Throughout our labours we have felt so strongly the necessity of obtaining numerical results as data for the foundation of a theory, that we have not hesitated to risk much in this cause. By the fusion of terminals, or the sudden discharge of the condenser, we have lost a vast number of very beautiful tubes; but gradually, by the adoption of various devices, and by the employment of instruments specially constructed and insulated to suit the high potentials we deal with, we have succeeded in overcoming the various impediments, so that we can now readily obtain values for the physical quantities that enter into consideration in our experiments.

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Die schiinen theorelischen Resultale, die sich in den lelzten Jahren aus einer genaueren Untersuchung des Indigos ergeben haben, machten ahnliche Erforschung anderer Farbsubslanzen in hohem Grade wiinschenswerth. Ich wahltu fur meine Versuche den Farbstoff der Cochenille, indem das Sludium dieses Korpers, auber wissenschafllichern Interesse, auch einige Ergebnisse von praktischeni Werthe versprach , besonders seit neuere Forschungen von P reifser eitie so innige Beziehung zwischen dem chemischen Verhalten des Indigos und dem einer Reihe rother und gelber Farbstoffe anzudeuten schienen. Ehe ich indessen die Beschreib.ung meiner eigenen Versuche beginne, hahe ich es fur zweckmabig, einen kurzen Umrifs der Resultate zu geben, die bis jelzt von den Chemikern, welche sich niit diesem Gegenstande beschaftigt haben, erhalten worden sind. Dr. J o h n *I scheint die erste Analyse der Cochenille ver-*) Tahlcaux chiniiques du regae animal. Annal. d. Chrmio u. fharm. LXIV. Rd. 1. Ifrft. i *) Aiinal. tle Chiln. et dc Pliys. 2. six. T. VlII p. 250 und Journ. de P a m . 2. ser. T. IV p. 193.

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XC. On Voltaic Electricity, and on the effects era Battery charged with Sulphate of Copper. By Mr. W. DE LA RYE**.