to his investigating the conditions of the eye on which colour-blindness or Daltonism depended. He published an article on the subject in the 'North British Review.'
In 1843 the conflict which had prevailed for ten years in the church of Scotland was brought to a close by 474 ministers retiring from the old church of Scotland, protesting against the grievances of church patronage. Brewster had taken part in every step of the 'long conflict,' as it was called ; he signed the Act of Protest ; with his elder brother he walked in the solemn procession which left St. Andrews Church on 18 May, and he attended every sitting of that first assembly of the Free church of Scotland. The prominent position taken by Brewster in this movement caused in 1844 proceedings to be commenced against him by the established presbytery of St. Andrews, aided by the university, to eject him from his chair. The case, however, was quashed in the residuary assembly because he had not signed the formal deed of demission.
For Professor Napier's 'Edinburgh Review' Brewster wrote twenty-eight articles. In 1844 the 'North British Review' was started under the editorship of the Rev. Dr. Welsh. Brewster became a regular and constant contributor. Professor Fraser, who was editor of the 'North British Review' in 1850 and the seven following years, says : 'He contributed an article to each number during the time I was editor, and in each instance, after we had agreed together about the subject, the manuscript made its appearance on the appointed day with punctual regularity ;' and Professor Blackie, who edited the 'Review' from 1860 to 1863, writes : 'Sir David Brewster was ever remarkable for the carefulness of his work, the punctuality with which it was delivered, never behind time, never needing to write to the editor for more time or more space - a model contributor in every way.'
On 27 Jan. 1850 Lady Brewster died and was laid to rest beneath the shade of the abbey ruins of Melrose. In April Brewster, with his daughter, went abroad for change of air and scene. He renewed his acquaintance with Arago, which had begun in 1814 ; he visited M. Gay-Lussac just before his death, and met the Swiss philosopher, M. de la Rive.
In 1851 he was president of the meeting of the British Association at Edinburgh. In his address he pleaded with much earnestness 'for summoning to the service of the state all the theoretical and practical wisdom of the country,' and for the extension of the advantages of education. 'Knowledge is at once the manna and the medicine of our moral being.' The pen of Brewster was singularly prolific. Between 1806 and 1868 he communicated no less than 315 papers on scientific subjects most of them bearing upon optical investigations to the transactions of societies, and to purely scientific journals. Beyond these he wrote seventy-five articles for the 'North British Review,' twenty-eight articles for the 'Edinburgh Review,' and five for the 'Quarterly Review.' The most lasting monument to his fame, however, will certainly be his beautiful investigations into the phenomena of polarised light. He shared also with Fresnel the merit of elaborating the dioptric system for the improvement of our lighthouses; and he divided with Wheatstone the merit of introducing the stereoscope, the lenticular instrument belonging especially to Brewster.
Besides the above he wrote in 1841 and 1846 'Martyrs to Science,' or lives of Galileo, Tycho Brahe, and Kepler ; and in 1854 an answer to Whewell's 'Plurality of Worlds' entitled 'More Worlds than One, the Creed of the Philosopher and the Hope of the Christian.'
In 1860 he was appointed vice-chancellor of the university of Edinburgh, and in that capacity presided at the installation of Lord Brougham as chancellor. Brewster in this year became an active member of the National Association of Social Science, and was afterwards chosen as vice-president. In this year he was made M.D. of the university of Berlin. He was at this time a frequent visitor to London, taking the greatest interest in the scientific societies of that city. In 1864 he was appointed president of the Royal Society of Edinburgh. In the spring of that year he was attacked, while residing in Edinburgh, with one of his seizures of prostrating illness, from which, although he appeared to rally, he never entirely recovered.
The 'lighthouse controversy' was to Brewster, in his latter days, a source of annoyance. It was a great comfort to him when the council of the Inventors' Institute in 1864, after examining the merits of the investigations made by Fresnel and others, reported that the introduction of the holophotal system into British lighthouses was due to the persevering efforts of Brewster. In June of this year a neglected cold fell heavily on Brewster's aged frame, and rendered him so feeble that he could not walk far, or labour in his library, without great fatigue. This state continued until 1867, when 'he was unable to play his quiet game at croquet.' Believing himself to be a dying man, he gave instruction to a young
