effects directly from a Wimshurst electrical machine, M. Le Bon from a petroleum lamp, Dr. A. Mau of Brooklyn from the sun. Their results, however, received no satisfactory confirmation. Dr. and Mrs. Huggins, on February 22, exposed a rapid plate, screened with a thin sheet of aluminium, to bright sunshine during an hour and a quarter without getting a trace of chemical action; and Professor Hale and M. Henri Becquerel have since fortified the conclusion that X-rays of solar origin are non-existent.

The truth seems to be that they make part of the phenomenon of fluorescence, and that certain kinds of glass, accordingly, lend themselves to their production. Hence arose a web of experimental contradictions, at first sight hopeless of disentanglement, the presence or absence of the glass in question unsuspectedly determining the results obtained. M. Charles Henry's discovery of the reinforcement supplied by sulphide of zinc to the novel agency furnished, nevertheless, a clue which has been successfully followed up. He found it to be an originating source of X-rays; M. Poincaré suggested that the same property might belong to all fluorescent substances; and his hint was promptly verified by M. A. d'Arsonval,* M. Becquerel,† and (perhaps we may add) by Mr. Lascelles Scott. Not every quality of fluorescence, however, is thus effective; it must be of the green-yellow kind shown by German glass. Of this material Crookes's tubes are made; and hence, we are led to believe, comes their efficacy in the production, under the bombardment of molecular torrents, of the enigmatical rays. We await with the deepest interest the further developments of their investigation.

* Comptes Rendus,' March 2, 1896.

See a letter in the 'Times' of March 10.

† Ibid.

ART.

ART. X.-The Queen's Prime Ministers. Nine Vols. London, 1890-95.

T is a trite remark that there is no portion of history so

I imperfectly

6

which immediately precedes their own participation in public affairs. The truth of this saying is vividly impressed by a perusal of the series of 'The Queen's Prime Ministers,' which has recently been published under the editorship of Mr. Stuart J. Reid. The authors of these nine biographies are all men who have taken part more or less directly in public life, and who are personally familiar with the leading events and characters of their own day. But it is impossible for anyone who is at all acquainted with the craft of book-making, to avoid the conclusion, that they have had one and all, in schoolboy phrase, to get up' the period on which they have undertaken to write. If so, they are not more ignorant than the average of their contemporaries. We are convinced that the majority of educated Englishmen would be less likely to make a mistake in reciting the roll of the Kings of England than they would be in repeating in their correct sequence the names of the statesmen who have held the office of Premier during Her Majesty's reign. We feel confident that if adult men of letters had to undergo historical examinations, they would run a smaller risk of being plucked if they were set to explain the causes of the Thirty Years' War, than if they were called upon to state the circumstances which led to the resignation of Earl Grey and the accession of Lord Melbourne in 1834. The cause of this ignorance is not any lack of interest in the period under consideration, but the absence of any comprehensive record of the century now drawing to its close. Various attempts have been made to write contemporary narratives of the England of to-day. Of these attempts Miss Martineau's Forty Years of Peace,' and Mr. Justin McCarthy's 'History of Our Times,' are, we think, the most successful; yet not one of them can lay any claim to be considered a standard authority. The plain truth is that all history to be of permanent value must be written at a considerable interval after the events narrated have occurred, and after both actors and spectators in the drama have passed away. A certain distance is required to judge of the perspective of political as well as of natura) objects. Writers who, like Greville, have left behind them their recollections, impressions, and appreciations of the public men of their day, have provided invaluable information for the historian