could have cited from Dr. Black, but do not think it

necessary.

But neither of these experiments will support the doctrine of latent heat in steam; I mean that there is nothing conformable to the explanations of the terms given above. That an abundance of caloric has passed through the water is admitted, and according to the last experiment is gone along with the water all boiled away; that is to say, this abundance of caloric has elevated the temperation of the water to such a degree that it is become volatile, and the water and the caloric have escaped into the atmosphere together. But if, as in the first experiment, this volatile water had been brought into contact with a quantity of cold water, or any cold body to which a proper instrument may have been applied, it would have parted with its proportionate degree of caloric, and the instrument would have shown the precise temperature of both, of uncombined caloric.

For notwithstanding all the address in conducting and detailing the experiment, no latent caloric has been brought into the account.

It is remarkable that the advocates for this opinion have successively been aiming to establish an incontestible precision in the results of their experiments, but are constrained to be satisfied with approximations at last; for here in the first experiment the quantum of heat is determined 950°; and another experiment brings it 954; and that above by Dr. Henry makes it 810°; and Mr. Pictet says it is 600, and Mr. Watt shewed it was 920°.

I will make every allowance for disappointments in conducting experiments where a mathematical precision is sought for; but the difference between Mr. Pictet and Dr. Black is inadmissible.

I remem

I remember when M. de Luc was giving evidence in the cause of Bolton and Watt against Bull, that he stated that it required six times as much caloric to evaporate a quantity of water as it would to bring it to boil, without fixing any precise temperature at the commencement, so that if it was 62° or 32° it seemed not to signify.

However, it is affirmed that 954° of caloric have passed into the water, and that it is contained in the vapour, which in correctness of expression is not true, but if I admit it, it will not prove the position. If any thing were to be proved that may be proved, it should be that so much caloric has entered the water, and that it has escaped, or it is there still: the latter cannot be, and I hope I shall not be accused of quibbling if I ask where then? the answer must be, gone mixed with the atmosphere, while the steam is no more.

Well, but suppose it had been detained in a vessel capable of preserving its temperature, then I say you would find it at 212: yes, you would say, that is the thermometrical temperature, but it has received 954°; granted, as to the aggregate quantity of its particles; but when we apply the term heat, whether latent or exposed to a body, it is to be understood as applicable to a part as to the whole, and therefore, a cubic inch of any body containing it must have the same degree as the whole mass. And will it be said if I take from this aggregate quantity of steam a cubic foot, for instance, that that cubic foot contains 954° of latent caloric, when you have stated that 10,000 cubic feet contain but the same quantity?

To be more particular; I will take two vessels capable of containing eight or ten atmospheres; in one the steam shall be generated, and in the other collected (preserving their temperature); and let a thermometer constructed VOL. XXV.-SECOND SERIES.

U

for

for high temperature be placed in the last or either of them, will it be said that the thermométrical temperature, all the while the experiment is going on, shall be no more than 212°, or will it not indicate the whole of the caloric taken up by the water? and if so, where is the la tent caloric? The whole of the above experiments then amount only to this, namely, that by them we obtain the quantum of caloric required to generate a certain volume of steam from a given quantity of water.

I am under some necessity of apologizing for the tedious præcognita of this paper, as it was suggested to me by a friend whose judgment I highly respect, but I could not comply with his intimation on these accounts: first, as I am no chemist, it is but proper that I should shew how I accept those terms which relate to this matter, for fear I may have mistaken their true acceptation; and secondly, because they will afford some information to any other tyro in the study of the subject.

Klippa, near Gotheborg,

Yours, &c.

J. C. HORNBLOWER.

February, 1813.

I

On the best Method of constructing a Peach House. By THOMAS ANDREW KNIGHT, Esq. F. R. S. &c. With an Engraving.

From the TRANSACTIONS of the HORTICULTURAL SOCIETY of LONDON.

SENT to the Horticultural Society, in 1808, a description of my vinery here, which I supposed to be so constructed as to receive the greatest heat, with the least expenditure of fuel, and to admit the greatest quantity of light, through the least extent of glass, at

those

those seasons of the year when light is wanted: and I then expressed a hope that some other members of the society would give plans for the proper construction of forcing houses, for other purposes. But as this has not been done, I take up my pen to offer some observations: on the most advantageous form and dimension ofà. Peach House.

Another gentleman, the rev. Mr. Wilkinson, has, however, subsequently undertaken to prove that the inclination of roof, which I have recommended, is, by no. means, the most advantageous; and it will therefore be necessary for me first to answer the objections he has stated. For silence, on my part, relative to those objections, would appear contemptuous, if I persist, as I do, in retaining every opinion, which I have given in that paper; particularly as the small deviation from my former plan for a vinery, in that I now recommend for a Peach-house, is in diametrical opposition to the theory and opinions of Mr. Wilkinson.

Mr. Wilkinson's first position is that "we want the genial warmth of the sun most in the spring:" he thinks about the sixth of April. The fires in a vinery rarely are, and never ought to be, lighted before the middle of February; and the application of heat ought then to be slow and gradual. The leaves will consequently be young and tender in the beginning of April, and will be very ill calculated to be suddenly exposed as they often must be, by the removal of intervening clouds, during the

* See the Horticultural Transactions of 1809.

Theoretical writers on vegetation are extremely apt to transfer some of the habits and feelings of animal life to plants; whence have arisen the frequent recommendations of poor soils, and cold situa tions, for nurseries; the writers feeling how agreeable it is to go from worse to better, and how disagreeable the contrary.

rapid variations of weather, and of temperature, in the end of March, and the beginning of April, to the full influence of the sun, falling vertically upon the glass. The wind is also often so cold, when the sun shines very brightly, at that season of the year, that much air cannot always be admitted without injury to those plants, with which it first comes into contact; and therefore, if very great attention be not paid by the gardener, the tender leaves and young shoots of the vines will be often injured; and indeed the young leaves and shoots sometimes fade much in my house, during hot days in the beginning of April, though the light does not fall vertically on the roof before the 20th of May. But waving wholly this objection, the stimulus of more light, than can subsequently be given, is always exceedingly injurious, in unnecessarily expending the excitability of the plants. Every year's experience shows how much better seedling plants grow in spring than in autumn. In the former period the intensity of light is increasing; in the latter it is decreasing, as it would be in a house constructed according to Mr. Wilkinson's recommendation, as far as inclination of roof would operate, from the 6th of April to Midsummer.

Mr. Wilkinson's next objection is, that the inclination of roof, which I recommended, admits most light and heat when they are "least requisite." Every gardener must know, I thought every man had known, even he who stands behind the counter in the obscurest alley in London, that fruits are always best, when heat and light are very intense during the period in which they are ripening, and that heat and light are then most requisite.

But it is not on the 21st of July only, that an inclination of roof of 34 degrees admits most light. I contend that the reflection of light continues to diminish, as the

solar