of the fluid beyond the expanfion of the glass veffel, fo our inftrument will fall by the excess of the fame expanfion, beyond the proper expansion of the materials it is compofed of. To measure the specific gravities of SOLID BODIES. The folid bodies, to be tried by this inftrument, muft not exceed 1000 grains in weight. Place the inftrument in distilled water, and load the upper fcale or difh, till the furface of the water interfects the middle of the stem. If the weights required to effect this be exactly 1000 grains, the temperature of the water anfwers to 60° of Fahrenheit's fcale; if they be more or less than 1000 grains, it follows, that the water is colder or warmer. Having taken a note of this weight, unload the fcale, and place therein the body, whofe fpecific gravity is required. Add more weight, till the furface of the water again bifects the ftem. The difference between the added weight, and the former load, is the weight of the body in air. Place now the body in the lower scale or dish under water, and add weights in the upper fcale, till the furface of the water once more bifects the ftem. This laft added weight will be the difference between 1000 grains, and the weight of the body in water. To illuftrate this by an example. N. B. The specific gravity of lead and tin, (and probably other metals) will vary in the third figure, when the fame piece of metal is melted and cooled a fecond time. This dif ference probably arifes from the arrangement of the parts in cooling more or less fuddenly. The load was found by experiment A piece of caft lead required the additional weight 999 : 10 grains. 210 : 85 788 : 25 Additional weight when the lead was in the lower scale 280 : 09 Difference is abfolute weight in air When the inftrument is once adjufted in diftilled water, common water may be afterwards used. For the ratio of the specific gravity of the water made ufe of to that of diftilled water being known (==), and the ratio of the specific gravity of the folid to the water made use of being also known (==), the ratio of the specific gravity of the folid to that of distilled water will be compounded of both (that is,). cb There is reafon to conclude from the experiments of various authors, that they have not paid much attention either to the temperature or specific gravity of the water they made use of of. They who are inclined to be contented with a lefs degree of precifion than is intended in the construction here defcribed, may change the ftem, which for that purpose may be made to take out, for a larger. One of the greatest difficulties that attends hydrostatical experiments, arifes from the attraction or repulfion that obtains at the furface of the water. After trying many expedients to obviate the irregularities arifing from this caufe, I find reafon to prefer the fimple one, of carefully wiping the whole inftrument, and especially the stem, with a clean cloth. The weights in the dish must not be esteemed accurate, while there is either a cumulus, or a cavity, in the water round the stem. I am, DEAR SIR, Your affectionate humble fervant, WILLIAM NICHOLSON. LONDON, June 1, 1784. MEMOIRS MEMOIRS of the late Dr. BELL, by JAMES CURRIE, 1785. GENTLEMEN, TH HE refpect which you have expressed for our late member, Dr. GEORGE BELL, by the Refolutions of the Society, which occafion this address, cannot fail to be highly pleafing to all those who honour his memory. To me this at * At a meeting of the Literary and Philosophical Society of Manchester, held February 4, 1784. 1. Refolved, as a mark of respect to the memory of George Bell, M. D. That a tranflation be made of his Inaugural Differtation de Phyfiologia Plantarum-That fome brief memoirs of the author be prefixed to it, and that the whole be inferted in the Journals of this Society. 2. That James Currie, M. D. the friend of Dr. Bell, and an Honorary Member of this Society, be requested to make the tranflation, and furnish the memoirs specified in the above refolution. 3. Refolved that a copy of these refolutions be tranfmitted to Dr. Currie, by the acting fecretary of the Society. tention tention is particularly grateful; and I should not have been fo flow in executing the task which you affigned me, had not long continued ficknefs deprived me of the power. Now that my ftrength is in fome measure restored, I embrace the earliest opportunity of presenting the translation which you have requested; and more fully to comply with your wishes, I fhall prefix a fhort history of the life of my much lamented friend. Dr. BELL was born at his father's eftate, in the county of Dumfries, in the autumn of the year 1755. He was the younger fon of Richard Bell of Greenhill, by Mifs Carruthers of Dormont; and, by both fides of the house, was defcended of families which claim high antiquity in that country, though little known to fame. The rudiments of his education he received at home, and he was very early diftinguished by the quicknefs of his apprehenfion, and the general brilliancy of his parts. While he was yet very young, he had the misfortune to lose his father, who died at Bath in the year 1766. This lofs was, however, in a great measure supplied by the care of his mother, who yet furvives to be a bleffing to her friends; and by the counfel and example of his brother, who, though very young, already difplayed an uncommon degree of prudence and virtue. By them, Dr. Bell was placed at the public fchool of Annan, then conducted by the Rev. Mr. Wright, in whofe house he |