In 1852 he introduced the mode of propulsion with two or double screws, now much adopted.

The fine establishment for making muskets at Constantinople was carried out by him, and he was constantly engaged in the construction of a great variety of machinery, such as steam-engines on a large scale, dredging-machines, millworks, breweries, &c. &c. . In 1850 he wrote a long report on the water-bearing properties of the Bagshot district, for the purpose of supplying London with water; in 1857 a paper to the Civil Engineers, on the history and method of making béton or concrete; in 1856, a report and project for improving the entrance of the river Mersey, read at the Cheltenham meeting of the British Association.

Besides actual works carried out, George Rennie was fond of making physical experiments on the different subjects he had to consider, the results of which he communicated to the societies of which he was a member. His experiments on the strength of materials, three years before those of Morin, are most accurate, and led the way to a proper knowledge of the strain to which different bodies may be safely subjected. They referred especially to the following subjects:-On resistance of fluids, on that of solid bodies in air and water; on friction; on the expansion and contraction of iron and stone arches; on canal traction; on the resistance of trains; on the development of heat by water in motion; on the resistance of screw propellers at different depths in the water. By these and by many other experiments did George Rennie add to that kind of knowledge which is as indispensable for the practical applications of engineering as it is important to general science.

Endeared as he was to a large circle of friends by his unassuming kindly spirit, no less than for his practical intelligence, a profound feeling of sorrow was caused by the announcement of the serious accident which, after many months' illness, terminated in his death.

HENRY DARWIN ROGERS was born at Philadelphia in 1809, the third of four brothers, who have all distinguished themselves in physical science. At an early age he undertook professional duties in Pennsylvania, and soon afterwards entered upon the long series of elaborate surveys with which his name will remain associated. It was especially in working at the great State-exploration of Pennsylvania, in union with his brother, Prof. William Rogers, who was charged with a similar task for Virginia, that his industry and breadth of view were strongly manifested. The brothers were supported by the aid of a numerous corps of assistants, and, striding in the course of a few years over an area no less extensive than full of interesting detail, were able, in 1842, to announce to a meeting of the American Association of Geologists their conclusions on the structure of the Appalachian chain, and this in a manner so lucid and vigorous as not only to charm the hearers present, but to rivet the attention of geologists in all parts of the world. Those who have enjoyed the advantage of hearing Prof. Rogers at a meet

ing of the British Association, or in our own rooms, or in general conversation, will long recollect the facility of expression and the occasional bursts of eloquence which would animate his treatment of favourite topics.

The great work of his life was the final Report on the Geology of Pennsylvania, a magnificent quarto filled with carefully collected details and illustrations of that great region, which embraces a great part of the most important mineral wealth of the United States. For the purpose of more readily completing his maps and plates Mr. Rogers betook himself to Edinburgh, and there established an intimate acquaintance with many members of the Scottish literary community. In 1857 he was invited to accept the Professorship of Natural History and Geology at Glasgow, which honourable post he retained until his death in May last.

For several years before his fatal attack, Prof. Rogers had been in delicate health, but had nevertheless made several journeys to America, and had continued at intervals his scientific and literary pursuits. Whilst employed in his great survey he had contributed to the Proceedings of this Society a paper entitled "Some facts in the Geology of the Central and West Portions of North America." A long series of Memoirs and Reports, published in the American scientific journals, have placed his name among the highest of the numerous excellent geologists who reflect credit on the United States. In 1856 he delivered a lecture at the Royal Institution, containing an admirable summary of the geology and physical geography of North America. In this address he dwelt specially on those great features which he had elaborated in his survey, the disturbance of the Paleozoic rocks of the Appalachian chain—“ a stupendous undulation, or wave-like pulsation, the strata being elevated into permanent anticlinal and synclinal flexures, remarkable for their wave-like parallelism, and for their steady declining gradation of curvature, when they are compared in any east and west section across the corrugated zone." To the westward of the Appalachian chain, where this strueture is conspicuous, he pointed out that "the crust-waves flatten out, recede from each other, and vanish into general horizontality." Coupled with these leading features, he remarked that the total thickness of the Coal-measures steadily diminishes from some 3000 feet thick in Pennsylvania to 1500 feet in the Illinois basin, and to not more than 1000 feet in the basins of Ohio and Missouri; and, similarly, the number of workable seams of coal dwindles from 25 on the Schuylkill to probably 7 in Indiana and Illinois, and but 3 or 4 in Iowa and Missouri. And when we add to this the clearly established facts of the increasing amount of sea-deposits simultaneously with the decrease of land-derived materials eastward, and the diminishing effects of metamorphism in the same direction, from the fully bituminous coals of the Western States to the hard anthracites of the most disturbed region, it must be conceded that Professor Rogers contributed a noble quota to the unravelling of some of the grandest phenomena which geologists have been called upon to investigate.

PERCIVAL NORTON JOHNSON, F.R.S., assayer, metallurgist, and refiner, of Hatton Garden, died June 1st, 1866, aged 73. He was the eldest son of John Johnson, at one time the only commercial assayer in London; and after working with his father for some years, he established himself in Hatton Garden half a century ago.

He rapidly rose to the highest eminence as an assayer and metallurgist, and his opinion was so much sought after that he could hardly get through the work which crowded upon him.

The extreme accuracy of his assays (viz. in reporting the actual contents of gold and silver, which before had only been done approximately) soon caused them to be called in question, and to be refused by the buyers of bullion, the advantage in buying upon them being less than upon the ordinary assays. Upon this being represented to him by the merchants, he at once stated that he was willing, if required, to purchase all bars upon his own assays. And this was the origin of his taking up the refining-business, thus, as it were, compulsorily thrown upon him. In this he was so successful that it has ever since continued to be a very important branch of the Hatton Garden business, and the largest of its kind in the world. His ability in this (as in all other branches that he entered upon) was soon recognized publicly; and when the gold bars from the Brazilian "Gongo Soco" mines, which came over in very large quantities, were refused at the Mint on account of brittleness, he was consulted on the matter, and undertook to refine and toughen them, in which he perfectly succeeded, and the whole of the Brazilian gold was from that time worked at Hatton Garden.

It was in this gold that he discovered the existence of Palladium; and having succeeded in its separation, he introduced it commercially, at once determining and making known the best uses to which it could be applied. At one time he was able to supply this metal at 14s. per oz.; it is now so scarce that it sometimes realizes ten guineas per ounce.

When the Geological Society determined, in 1846, to employ this interesting and rare metal for the Wollaston medal, they applied to Mr. Johnson to supply it, and he generously responded by making it a pleasure, for many years, to present it gratuitously to the Society.

He

After he had been in business some years, he visited Germany, and was much interested in the mining-operations of certain districts there, to which he gave special attention. It was at this time that he met with the compound alloy called "German silver," then in a very crude and imperfect state of manufacture. brought over with him some of the substance, analyzed it, and upon the basis of his analysis commenced its manufacture, with much profit to himself. He was the first person in England who actually made it; and he carried on its manufacture and introduced it to general use, laying the foundation of the enormous business which has since arisen in this branch of metallurgy.

At that time the rough Pottery Nickel was merely ground and

ignited with nitre, the resulting oxide washed and reduced, at the same time that the fusion of the alloying metals was effected.

After a few years, owing to his many engagements and the pressure of what he considered his more legitimate work, he ceased to apply himself so diligently to the German-silver business, and it was then most energetically taken up by the Birmingham firm, Evans and Askin, who have ever since retained it almost exclusively in their hands.

It was about this time that he was much engaged in miningpursuits, and was consulted upon, and visited professionally, nearly all the mining-districts in England and Wales, as well as many important ones abroad. He was the first to introduce in Cornwall the German shaking and washing table, with modifications of his own. Residing during a part of the year at Ward Cottage, beautifully situated on the banks of the Tamar, he was able to make frequent visits to the interesting although shortlived mines of the district of Callington, and to those of Calstock and Beer Alston. He will always be remembered throughout the mining-districts for his great kindness and consideration towards the miners, whose social condition it was his constant aim to improve. At great expense to himself he erected schools &c. in the neighbourhood of the mines, and took an active part in their supervision. He also used his utmost endeavours to alleviate the toil of the miners in ascending and descending mines: with this view, as well as for the improvement of the ventilation, he, at the Tamar mines, made the experiment of a sloping gallery, which ran for a considerable distance under the river, by which means the miners could walk up and down without the use of ladders.

Amongst his many minor chemical discoveries may be mentioned several pottery colours, amongst them the rose-pink, at a time when that colour was much wanted in the potteries, the manufacture of which he carried on for many years, at the same time as "oxide of uranium," a valuable colour much used in glass-making, of which he always maintained the monopoly.

Mr. Johnson alloyed, melted, and assayed the trial-plate of the Pyx, which is the criterion of the quality of the coin of this country, and which is still kept in the Lord Chancellor's office.

His greatest success, however, and that which has proved the most valuable to the progress of chemistry and manufacture generally, was the treatment of platinum. To him undoubtedly belongs the credit of having been the first after Dr. Wollaston who successfully refined and manufactured that metal upon a commercial scale, and introduced it for many of the valuable purposes to which it is specially adapted. The first large and perfect sheet of pure platinum ever produced was made by Mr. Johnson at 79 Hatton Garden; and seeing the immense importance of this metal, he ever afterwards made it his speciality.

As narrated by Percival Johnson, it is an interesting and perhaps not well-known fact that the discovery of the mode of refining and consolidating platinum was disputed with Dr. Wollaston by

Mr. Thomas Cock, a brother-in-law of Mr. Johnson's, a gentleman of considerable private means, and an able although comparatively unknown amateur chemist and metallurgist*. It was in William Allen's laboratories, Plough Court, that he first succeeded in working the metal; and it was at Mr. Allen's special request that he showed his experiments and their results to his friend Dr. Wollaston, then visiting him. Dr. Wollaston adopted an almost identical process for the manufacture of platinum; and to him has generally been accorded the credit of having discovered it.

Mr. Thomas Cock being much interested in the work at Hatton Garden, spent much of his time in the laboratories there. Mr. Johnson took up the platinum-manufacture, using Mr. Cock's process up to the time of his retiring from business, and always remained the only platinum-refiner in England.

His eminence as an analyst should also be noticed. So great was it, that the only other commercial assayers in London, though his rivals, used frequently to send him compounds or minerals of a difficult and complicated nature to report upon for them.

Probably no man has attained in his day greater perfection in whatever he undertook, or was more looked up to for his opinion; and few have worked with greater perseverance, or done more for the advancement of their profession.

For several years prior to his death Mr. Johnson resided in a pretty cottage, which, with an estate, picturesquely overlooking the sea, he had purchased at Stoke Fleming, near Dartmouth. Although near the scene of his former mining-adventures, and still working in his well-appointed laboratory, he was repelled from further participation in the mines by the conduct of some of his associates. His withdrawal was felt as a serious loss both by the working class whom he had befriended, and by the owners and managers of mineral property, to whom he had rendered himself remarkable, amid so much of dishonest and careless speculation, by his intelligent and honourable conduct of affairs; nor is it too much to say that enterprise in our western mines would take a much higher position if more of its leaders emulated the manly tone and liberal uprightness of Percival Johnson.

By the death of CHARLES MACLAREN, which took place in September last, we have lost one of the veterans of geology, and a man who did much, in a persevering but unobtrusive way, to render the principles and aims of the science known to a large section of his countrymen.

He was born in the village of Ormiston, in the county of Haddington, on the 7th October, 1782, and at an early age, after some few years of parish schooling, was intended to be apprenticed to his uncle, a smith in a large way of business. But as his constitution proved to be delicate, he followed for a time the occupation of a clerk and book-keeper with some Edinburgh firms, and employed his spare hours in diligently acquiring a knowledge of Greek and * See Aikin's 'Dictionary of Chemistry,' 1807.