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Appearance of clouds on the



and 20th of May.


Observations in Illustration of Mr. HOWARD's Theory of
Rain. In a Letter from THOMAS FORSTER, Esq.




S the following observations may serve farther to illustrate Mr. Howard's ingenious Theory of Rain, (see his paper on the modification of clouds,) I shall request your insertion of them in your scientific Journal.

On the 18th inst. the day was close and warm, in the afternoon I observed several different modifications of cloud dispersed about in the atmosphere at different altitudes. In some places cirro-stratus might be distinguished; in others, the clouds shewed a tendency to cirro-cumulative aggregation, cumuli increased in density, and cirrose fibres transversely crossed their summits, forming cumulo-stratus, which like mountains transfixed by the mighty shafts of giants appeared in the horizon, and represented a majestic appearance; while in other places the process of nimbification appeared going on rapidly, and distant thunder was heard. About six o'clock the sky, seen between the clouds under the descending sun, appeared of a very unusual brownish lake colour. As the evening advanced the mountainous clouds in the horizon appeared of a deep blackish blue colour, their edges as well as those of other detached clouds above them exhibiting a bright golden colour. Flocks of cumulus floated along in the wind, and refracted dark lake coloured light; by degrees all the clouds lost their distinctive characters as separate modifications, and became one dense mass, which ended in rain during the night.

On the 19th it rained all the morning, but held up in the evening; the continuous sheet of cloud however remained, notwithstanding a strong wind from the north.

Early on the morning of the 20th the same uniform sheet of cloud obscured the sky. As the day advanced it broke, and this dense sheet of nimbus, which had been originally formed by the collapse of several distinct modifi


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cations, appeared to resolve itself into them again; as the sheet broke part of it seemed to mount up into a higher and comparatively calm region, and formed itself into eirrocumulus, in some places disposed like windrows of hay, in others consisting of small roundish nubecule of various sizes; and into cirro-stratus, consisting either of flat sheets of thin vapour with dentated edges, or disposed in streaks: other parts of the once continuous sheet of nimbus descended into a lower region, and floated along in flocks of cumulus, with a strong wind, and the day became very fine. In the evening the distinct modifications again seemed lost in a general mistiness of the atmosphere, which as it became darker seemed very red coloured, and this vapour was seen to thicken in particular places which became dense nimbi again, and gave forth vivid flashes of lightning, and thunder storms continued through the night.

From the evident decrease in the quantity of cloud during the fine part of the day, it is evident, that, while part of the sheet of nimbus, which obscured the sky in the morning, divided itself again into the several modifications, the collision of which originally formed it; great part must have been absorbed by the air: this is farther probable from the great transparency and dense blue colour of the sky between the clouds.

The insertion of these observations in your next number will, if convenient, oblige your constant reader,

Clapton, Hackney,

May 21, 1811.



Observations on Dr. BOSTOCK's Review of the Atomic
Principles of Chemistry. By JOHN DALTON.



DR. Bostock's dissertation on the atomic system of che-Dr. Bostock's mistry in your Journal (Vol. XXVIII, page 280) may be remarks on the

See Mr. Van Mons's paper in your Journal for September, 1809;

also Rees's Cyclopedia, article Cloud.


atomic system divided into two parts; one of which relates principally to of chemistry. the theory of chemical combinations, which I have embraced

Meaning of the terms, theory and hypothesis.

from an extensive comparison of facts and observations furnished by the writings of others, and from a careful and laborious train of experimental investigation of my own; the other relates to his application of the theory to the solution of a few of the more simple and common combinations. On the former of these parts I beg leave to make a few observations; on the latter I think it is altogether unnecessary to say any thing, unless it be to correct a misrepresentation or two which Dr. Bostock has accidentally introduced, namely, that oxigen and hidrogen in water are as 85'7 to 14.3 in weight, and that these numbers are as 7 to 1 nearly (page 285); and that I conceive nitrous oxide to be a binary compound (page 290). The weights of oxigen and hidrogen in water are stated (vid. New Syst. p. 275) to be 87.4 and 12.6 respectively; and it is nitrous gas which I maintain to be binary, and nitrous oxide and nitric acid to be ternary compounds.


I do not exactly agree with Dr. Bostock as to his remarks ou the difference between theory and hypothesis; these terms as far as I can learn from their common use differ only in degree. Theory is all or the greatest part of the facts reduced to regular laws; hypothesis is where only a few facts are reduced to laws, and the rest are either irreducible, or are yet only in a train, or have their accuracy suspected. I think no one would seriously advance any hypothesis on any subject, that had not some one or more facts previously established in its favour. What is theory to one man may be hypothesis to another. Newton had lived in an age when no mathematician but himself existed, he might have established his beautiful theory of gravitation to his own satisfaction; but it must have been only an hypothesis to the rest of his contemporaries. These observations lead me to remark farther, that my chemical doctrine on combination is not, “altogether hypothetical," according to Dr. Bostock's own definition. I remember the strong impression which at a very early period of these inquiries was made by observing the proportion of oxigen to azote, as 1, 2 and 3, in nitrous

dxide, nitrous gas, and nitric acid, according to the experiments of Davy. And Dr. B. must confess, that the greater part of the facts I have stated in my book, as the grounds from which I draw my conclusions, are not new; but facts that have been investigated by others before me, and often with the same results.

Dr. Bostock must be aware, that in writing my System of Chemistry, I have presumed all along, that the future readers of it would be tolerably acquainted with the various branches of the mechanical philosophy; otherwise I must have made a cyclopedia of it; one department must have treated of statics, another of dynamics, another of hydrody namics, another of pneumatics, &c. This was not my design. If therefore I have announced certain rules as proper to be laid down, and have given no demonstration of them, it was because they were deemed obvious to the class of readers I expected, or otherwise were such as could not be demonstrated but by the gradual developement of the system itself in its progress.

Mr. Dalton's

I proceed now to point out the mechanical consistency Mechanical of the 1st rule, which Dr. Bostock has quoted, page 283, consistency of namely, that "when only one combination of two bodies first rule of can be obtained, it must be presumed to be a binary one, combination. unless some cause appear to the contrary"; and if this be established, the other three which he quotes may be considered as corollaries from it.

Let us suppose a mixture, for instance, of hidrogenous Instance in the and oxigenous gas, in such sort, that there are the same of water. composition number of atoms of each gas; now as the gasses are uniformly diffused, each atom of hidrogen must have one of oxigen more immediately in its vicinity. The atoms of hidrogen are all repulsive of each other; so are those of oxigen: the atoms of hidrogen are all equally attractive of those of oxigen, and the attraction increases in some unknown ratio as the distance diminishes. Heat, or some other power prevents the union of the two elements, till by an electric spark, or some other stimulus, the equilibrium is disturbed, when the power of affinity is enabled t come the obstacles to its efficiency, aud a chemical union of the elementary particles of hidrogen and oxigen ensues. VOL. XXIX.-JUNE, 1811. Now



of water.

Instance in the Now the question is, whether, according to the received laws of motion, each one atom of oxigen should unite to the one of hidrogen next to it, or whether 7 atoms of oxigen should leap over all the more proximate atoms of hidrogen. to another at a greater distance, and consequently less attractive, and that finally only 4th of the number of atoms of hidrogen should be engaged by the oxigen and the rest remain in a state of freedom as before. The former is the conclusion I adopted, and thought it would scarcely require any elucidation; the latter is thought by Dr. Bostock equally plausible as the former (page 291). However till it can be shown, that a less force can overcome a greater, I must refuse my assent. Besides there is another consideration, that has no small weight with me; it is known, that the oxigen carries the greater part of its heat, and in all probability of its repulsion along with it in its combined state; it would therefore be an odd phenomenon, if it could be rendered vi sible, to see 7 atoms of oxigen surrounding 1 of hidrogen of equal size, all the atoms of oxigen repelling one another, but retained by an atom of hidrogen at the centre, whilst a number of atoms of hidrogen are around, all equally attractive of oxigen with the one engaged. But the difficulty does not end here: though I am persuaded the relative weights of the hidrogen and oxigen in water are nearly as 1 to 7, 1 by no means assert, that they are accurately so. Perhaps Dr. Bostock would prefer the ratio of 15 to 85; that is, in the smallest integers, 3 to 17. Now upon this view of the subject we must picture to ourselves 3 atoms of hidrogen surrounded by 17 of oxigen as constituting 1 atom of water; the remaining 14 atoms of hidrogen must be conceived to continue in their elastic state as spectators, and not to disturb the equilibrium of the atom of water. This may be the constitution of an atom of water; but it is wonderful, that in the decomposition of it by galvanism, nothing but hidrogen and oxigen should be, produced, and never any new combination should arise out, of so complex a system of particles as an atom of water exhibits to view. Would it not have been an improvement to have formed a set of atoms on purpose for water, by melting 3 of hidrogen into one, and 17 of oxigen into one? Both you and your readers will probably think by this

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