find, that as the demand increases, the tobacconists weaken It ought to be sufficiently what they send out; and care must therefore be taken, that strong. it be sufficiently strong when used, which may be known by its giving the water a tolerably brown colour. I have found sometimes a wine-glass full sufficient for a gallon of water; at other times, what I have procured has been so much diluted by the tobacconist, that it has required a pint to give a proper strength to that quantity. I was last summer greatly annoyed by the red spider on those trees that had a Red spider, direct south aspect. The minuteness of the insect, and being so securely sheltered underneath the leaf, prevented several of my applications from taking a due effect; but on watering my trees with an engine for about ten successive evenings, very forcibly, and immediately after being so watered giving them whilst wet a sprinkling of tobacco water, about three of those evenings, the trees recovered and ripened their fruit very finely. I hope next summer to have it in my power to inform you Apple trees of the result of an experiment I am now making, with respect transplanted. to transplanting apple trees from an orchard near me, that is about to be converted to some other purpose. Having purchased as many of the trees as I was desirous of remov ing, I have newly planted out about forty of them, several of which bare each a hogshead of cider last year, and have done it in many previous seasons, As I have paid great attention to the preservation of them, I have little doubt of success. But as it cannot yet be ascertained, I shall defer enlarging upon the subject till I have the pleasure of addressing you again. In the mean time I remain with great respect, Your most obedient servant, ROBERT HALLETT. Mr. Vince's pamphlet on the cause of gravitation. Cannot be the pressure of a medium vary as some power XI. Remarks on a Pamphlet, lately published' by the Reverend S. VINCE, respecting the Cause of Gravitation. By a Correspondent. SIR, To Mr. NICHOLSON. It is not long since I first saw Mr. Vince's pamphlet respecting Sir Isaac Newton's conjectures on the cause of gravitation; some parts of it appear to me so erroneous and so injudicious, that I think it right to take the first opportunity of expressing the disapprobation, which the author seems to deserve. After having shown, that the established laws of gravitation cannot be derived from the pressure of a medium, of ing in density which the density varies simply as any given power of the of the distance, distance, Mr. Vince proceeds in these words (P. 21), "It may be supposed, that if the above assumed law of density of the fluid will not answer the required conditions, yet some other law of density, which is compounded of different powers of the distance, may be made to agree with the law of gravity. Let us therefore represent the density of the medium by Pa" + Q a2 + R a3 + &c.-Hence, according to the foregoing reasoning (taking only the two first terms of the series), the law of force tending to the sun is 2q-qn 2q-qn 1 + Q xa His mistake pointed out. 2 m-m n Se xa 2 2 mm n PX 3 e 1+ R, &c. Now these, being different powers of the distance a, the whole can never constitute a power which varies as 1 a2 On this point the Professor's whole demonstration. rests, and it is difficult to imagine how he could have committed so palpable a blunder. We have only to put m=0, and Ro, in order to show the fallacy of his reasoning: the force will then be respresented according to the expression here laid down, by Q × 29-qn 2q-qn 3e 2 1, and -1 may become = 2 on many suppositions, while -- the the density is expressed by two terms of the first series. But in fact there appears to be another mistake in Mr. Vince's Another ercalculations, for instead of 2 m and 2q, he ought to have written 3 m and 39; Mr. Vince says, "let the density be as 1 rour. sertion. d", then the distance of the particles is as " (p. 17): Newton on the contrary, says, "particularum distantiæ Newton's aserunt ut cuborum latera A B, ab, et mediorum densitates reciproce ut spatia continentia A B cub. et ab cub.” II. 23. So that if the density be expressed by P-2, π being -1, which is the power of the distance of the particles of an elastic medium expressing their repulsive force, the law of the derivative force will be represented by Seat. 2Q These errours in the work of a Professor of Astronomy and Experimental Philosophy, and a Professor in the University of Cambridge, afford no very flattering specimens of the mathematical attainments of this country: and 1 am sorry to say, that they have been passed unnoticed by one of Mistake unnothe most respectable of our reviews, in which a copious account of the essay is inserted. "If the salt has lost its savour, wherewith shall it be salted?" Et quis custodiat ipsos Custodes ? ticed by the Review. Mr. Vince has thought proper to complain, in his prefa- Complaint of the author tory statement, of the conduct of the Council of the Royal against the Society, and in particular of that of its President, in de- Royal Society. elining to publish his essay in the Philosophical Transactions. He says, that it was presented by the Astronomer Royal to the Society, "when the President and one of the Secretaries requested, that the author would withdraw it, and present it again in the November following, as the paper appeared a proper subject for the Bakerian Lecture. It was accordingly withdrawn, and offered again at the time when it was requested to be presented. The paper was then read, and appointed to be the Bakerian Lecture. But before it went into the Committee which is expressly appointed to examine and determine what papers shall be printed, the author was informed, that it was doubtful whether his paper would be published. The circumstances attending this inVOL. XIX-APRIL, 1809. formation X The Society vindicated. Farther re marks. formation led him to suspect, that it would not appear in the Transactions of the Society, and in this he was not disappointed." In the whole of this important history there appears to me nothing whatever, that an impartial person could deem a just cause of offence. The author had more than once before been appointed to give a Bakerian Lecture; and when he offered this paper to the Society, "the President and one of the Secretaries" probably thought it a compliment due to his established reputation, to suggest to him, that it might serve for a Bakerian Lecture, without having gone farther than the title of his paper. He accordingly accepted the compliment and the fee. The paper having been partially read, as all mathematical papers must be, it is natural to suppose, that it was submitted to the examination of some one or more individuals, previously to its being discussed by the Committee of papers, since mathematical demonstra tions cannot easily be examined by any large body of persons, however select; and as the opinion of such individuals might easily be expected to influence the determination, of the Committee, it is not difficult to imagine, that it might be known beforehand, "that it was doubtful whether the paper would be published," although it may be questioned, whether or no the person who gave the hint acted with perfect discretion. After these remarks on the mathematical parts of Mr. Vince's paper, and this attempt to explain the conduct of the Council of the Royal Society, it will scarcely be necessary to make any comment on, the unjust and illiberal insinuation conveyed by the observation, that "Sir J. Pringle, the late worthy and learned President of the Royal Society, executed the duties of his high office with great impartiality and honour." Nor shall I enlarge at present on any other objections which might be made to Mr. Vince's essay: what he says respecting the interference of the ethereal atmospheres of the different planets is totally foreign to the question; and some others of his remarks, which are perhaps better founded, have already been stated by Professor Robison, and by other authors: but these are imperfections which might easily be forgiven, if they were the only errours that have been committed in the essay. Farther Experiments and Observations on Potash and its Base. DEAR SIR, To Mr. NICHOLSON, Derby, March 28th, 1808. IN your Journal for February of this year, I communica- Detonating substance pro ted an account of some experiments, made, in company with duced from my friend Mr. James Oakes, with a view to produce the me- potash. tallic base of the alkalis, discovered by Professor Davy. In consequence of our not having sufficient galvanic power at that time, we did not succeed in separating the globules of metal from the potash, although we produced a substance, which detonated with a bright flash, when presented to water. We have however since repeated the experiments, with Completely se increased power, and have completely succeeded in producing parated from it. the metal, detached from the alkali, in which it is imbedded. The result of these additional experiments I should, according to promise, have communicated for insertion in the succeeding number of your Journal; but, observing, both in your, and other periodical works, that the same result had been obtained by others, I conceived any farther detail unnecessary: as however we have paid attention to the production of the black matter alluded to in my last, which ap- Black matter pearance has not been observed by any other experimen- accompanying talist, I have thought proper to make a few additional re marks. it. After repeating the experiments several times, we ascer- Formed at the tained the curious fact, that the black matter was formed at copper end only. |