gestions of great importance: first, that small amounts of impurity in a metal do not by their direct action produce the remarkable changes in physical properties to which their presence corresponds, but that they cause the metal with which they are alloyed to assume an allotropic form; and secondly, that in most cases alloys must be considered as ‘solidified solutions.’ In 1868 Matthiessen was appointed lecturer on chemistry at St. Bartholomew's Hospital in conjunction with Professor Odling; on the latter's resignation in 1870 he became sole lecturer. In 1869 he was awarded a royal medal by the Royal Society ‘for his researches on the electric and other physical and chemical properties of metals and their alloys.’ Besides his other work he had a large private practice as a consulting chemist, and from January 1869 to June 1870 was one of the editors of the ‘Philosophical Magazine.’ In 1870 he was appointed examiner to the university of London. On 6 Oct. of the same year he committed suicide, his mind having given way under severe nervous strain. At the time of his death he was occupied with the experiments on the chemical nature of pure cast-iron, of the committee appointed to inquire into which he was a member, and also with experiments with a view to the construction of a standard pyrometer. The ‘Royal Society's Catalogue’ contains a list of thirty-eight papers published by Matthiessen alone, and of twenty-three published conjointly with Von Bose, Burnside, Carey Foster, Hockin, Holzmann, Russell, Szcepanowski, Vogt, and Wright. The most important appeared in the ‘Philosophical Transactions’ and ‘Proceedings’ of the Royal Society, the ‘British Association Reports,’ ‘Journal of the Chemical Society,’ and ‘Philosophical Magazine,’ from which many were reprinted in foreign periodicals. Matthiessen's researches show remarkable acuteness, experimental skill, and conscientiousness, together with a distinct power of generalisation. That with his physical defect he should have accomplished so much delicate and exact work is a proof of rare perseverance. Matthiessen bore a high personal character among his contemporaries.
[Besides the sources already quoted, see Times, 8 Oct. 1870; Nature, ii. 475, 517; Pharmaceutical Journal, [3] i. 317; Chemical News, xxii. 189; Journ. Chem. Soc. 1870, p. 615; American Journal of Science, [3] i. 73; Proc. Roy. Soc. xviii. 111.]
MATTOCKS, ISABELLA (1746–1826), actress, was the daughter of a low comedian named Lewis Hallam, who acted at the older theatre in Goodman's Fields (not to be confounded with the Goodman's Fields theatre), of which his brother William Hallam, founder of a theatrical ‘dynasty’ in America, was manager. At this house, sometimes known as the New Wells, Leman Street, Goodman's Fields, there were three Hallams, Hallam sen., Lewis Hallam, and George Hallam (Genest), besides a Mrs. Hallam. The relations of the various members of this family, or families of this name, have received much attention in America, but nothing very definite is known. The ‘New Monthly Magazine’ for 1826, in a eulogistic article full of errors, speaks of the Hallam killed by Macklin as her father, which he was not. He does not appear even to have been her grandfather. Mrs. Hallam, who became in America by marriage a Mrs. Douglass, was a relative of Rich of Covent Garden, and was the mother of Isabella Hallam. Left behind by her father and mother upon their departure for America, Isabella was educated by her aunt, Mrs. Barrington, also an actress. She is said to have played at Covent Garden, when four-and-a-half years old, the part of the Parish Girl in ‘What d'ye Call It?’ and, not long after, the child in ‘Coriolanus.’ Her first traceable appearance is, however, given vaguely by Genest, 1752–3, at Covent Garden, as the Duke of York in ‘King Richard III.’ On 14 Feb. she was Page in the ‘Orphan’ to the Monimia of Mrs. Bellamy, 10 Dec. 1754; the child in ‘Coriolanus,’ assigned to Thomas Sheridan, 19 Feb. 1757; Page in ‘Rover.’ Mattocks, subsequently her husband (d. 1804), appeared for the first time at Covent Garden as Macheath, 1 Nov. 1757, and on the 5th Miss Hallam played the Boy in ‘King Henry V.’ On 22 April 1757 she was Robin in the ‘Merry Wives of Windsor,’ her aunt, Mrs. Barrington, being Mrs. Page. On 10 April 1761, for Barrington's benefit, she played Juliet to the Romeo of Ross. She was announced as ‘a young gentlewoman, being her first appearance (as a woman).’ She repeated this performance 22 April 1762. In 1762–3 she was regularly engaged, playing Dorinda in the ‘(Beaux) Stratagem,’ Isabella in the ‘Wonder,’ Isabinda in the ‘Busy Body,’ Parisatis in the ‘Rival Queens,’ the Princess in ‘King Henry V,’ Serena in the ‘Orphan,’ Selima in ‘Tamerlane,’ Sylvia in the ‘Recruiting Officer,’ Narcissa in ‘Love's Last Shift,’ Angelica in the ‘Constant Couple,’ the Lady in ‘Comus,’ and Miss Hoyden, and being the original Lucinda in Bickerstaffe's ‘Love in a Village,’ 8 Dec. 1762. Teresia in the ‘Squire of Alsatia,’ Isabella in ‘Wit without Money,’ Nysa in ‘Midas’ were added to her repertory the following season, in which also she was, 9 Dec. 1763, the original Nancy
