The discovery of the circulation of the blood in animals was soon followed by conjectures concerning the existence of a like circulation in the sap of vegetables. These conjectures gave rise to the first improvements in vegetable physiology, which may be dated from the appearance of a set of queries concerning the motion of the juices of plants, published in the Philosophical Transactions, anno 1668. These queries immediately engaged Dr Beale and Dr Tonge, and afterwards Dr Grew, Mr Willoughby, Mr Ray, and Dr Lister, to enter upon the subject; who, in a great variety of observations, struck out the first considerable discoveries in the vegetable œconomy.

There is an atmospherical appearance which is not explained by the known laws of heat and cold. It is the breath of animals becoming visible, in being expired into an atmosphere which is cold or moist; and the transformation of transparent steam into the state of mist, when mixed with air which is of a colder temperature. Natural philosophers have certainly considered these appearances as being explained in the general law by which heat and cold are communicated among contiguous bodies, otherwise they would have endeavoured to point out this particular law, which seems to depart from a more general rule, or does not follow the natural course of things observed on other occasions. The subject of this paper is to investigate a certain rule which, in the case now mentioned, may be discovered as directing the action and effects of heat and cold; and to form a theory of rain upon that investigated rule, concerning the evaporation and condensation of water.

Though the labours of M. De Luc, and of the excellent observers who followed him, have brought the barometrical measurement of heights to very great exactness, they have not yet given to it the utmost perfection it can attain. Some causes of inaccuracy are still involved in it; of which we ought, at least, to estimate the effects, if we cannot correct them altogether. The allowance made on account of the temperature of the air, implies in it a hypothesis that has not been examined, nor even expressed, and many other circumstances that affect the denfity of the atmosphere, have either been wholly omitted, or improperly introduced. The object of the present paper is to correct, the errors that arise from these causes, or, where that cannot be done, to assign the limits within which those errors are contained.

By the introduction of letters into algebra, to denote all the quantities, both known and unknown, involved in an equation, this very important advantage was gained, that the final equation exhibited both a general rule for the solution of all similar problems, and also the limitations within which such problems were possible.

In the seventieth and seventy-first volumes of the London Philosophical Transactions, the reader will find an account of some Experiments and Observations made here upon cold in the years 1780 and 1781.

Though, at first, I had no other view but that of keeping a register of the very cold weather which set in on the 13th January 1780, yet I was soon led to extend the plan of my observations, upon meeting with a new phænomenon, which appeared to me to deserve some attention. This phænomenon consisted in a constant difference of temperature of the snow which, at that time, covered the fields, and that of the air at a few feet above: the snow being the coldest.

In an age like the present, when few things in nature feem to have eluded the researches of philosophy, when the communications of learning are as well established as those of commerce, it may appear somewhat surprising, that one of the most important productions of milk should still remain, in a great measure, unknown to the most enlightened parts of Europe.

Problem

Having the apparent distance of the Moon's centre from a fixed Star, or from the centre of the Sun, together with the apparent altitudes of their centres, to find the true distance.

Solution

The difference between the apparent and true altitudes, and the angles which the Moon and Star make with the zenith and each other, must be known before the several corrections of distance are computed.

I Did not return from the excursion on which I was when I had the pleasure to see you at Dundee till last Tuesday night. On my arrival, I found your letter respecting the phænomenon that lately happened in this neighbourhood. Although ill qualified to give you satisfaction upon this subject, I shall, however, comply with your desire, and give you the most accurate account of that phænomenon which I have been able to obtain.

In the register from which this abstract is taken, the numbers were marked every day at nine o'clock A. M. The quantity of rain was measured by means of a tin-cylinder, guarded by a wooden box, and sunk in the earth, into which the rain was received through a funnel, whereof the area was quadruple that of the cylinder. A gage, which floated on the surface of the water in the cylinder, had a rod fixed to it, divided into inches and tenths, which passed through the pipe of the funnel. The fourth part of the rise of this index marked the depth of rain which had fallen since the last observation, and these observations were generally made once in twenty-four hours.

When we trace the parts of which this terrestrial system is composed, and when we view the general connection of those several parts, the whole presents a machine of a peculiar construction by which it is adapted to a certain end. We perceive a fabric, erected in wisdom, to obtain a purpose worthy of the power that is apparent in the production of it.