showed, was strongly diamagnetic, being only inferior to bismuth in this respect; and Dr. Matthiessen had determined that its power of conducting electricity was very near that of lead. It is precipitated from its solution by means of the battery in beautiful crystals, the form of which has not yet been determined; and when the experiment is carefully conducted, these spread over the dish in branches like a delicate seaweed, or with a stronger solution like the club-moss. The atomic weight of thallium is about 203. Its chemical properties are at first sight rather anomalous, and seem to justify the remark of M. Dumas, that it is the ornithorhynchus of metals. That eminent French chemist ranks it with the alkaline metals, with which indeed it has some common properties: but the speaker is inclined to class it with the heavy metals, lead and silver, to which it seems more nearly allied both by its chemical and physical properties: several of the chemical reactions of thallium were shown in corroboration of this view. Like the metals potassium and sodium, it forms a soluble oxide which is endowed with strongly alkaline properties; like them too it is not precipitated by sulphuretted hydrogen, nor in its lower state of oxidation by an alkali; it also forms an insoluble platino-chloride, but here the resemblance ceases. All the other reactions are similar to those of the heavy metals. The soluble oxide is in reality also allied to the oxides of silver and lead (which are both soluble in water and alkaline), inasmuch as it has no affinity for water, being rendered anhydrous even at the common temperature in a vacuum. It is readily precipitated in the metallic form from its saline solutions by zinc. It forms an insoluble peroxide, sulphide, iodide, bromide, chromate and sulphocyanide, and a slightly soluble protochloride, sesquichloride, ferrocyanide and chlorate.

The alloys of Thallium have not yet been much studied. Th euses of the metal the speaker said he was hardly yet in a position to dwell upon. At present it would appear only to confirm in the most striking manner the value of spectrum analysis as a guide in chemical research. As an agent for the production of colour in pyrotechny, it was only equalled in brilliancy by the two other elements which give a monochromatic light, lithium and sodium. The speaker here illustrated the monochromatic nature of the thallium light, by throwing the magnified image of its electric arc on a bouquet of variously coloured flowers; and concluded by thanking the audience for the indulgence they had extended to his first public discourse.

[W. C.]

Royal Institution of Great Britain.

WEEKLY EVENING MEETING,

Friday, February 6, 1863.

COLONEL PHILIP JAMES YORKE, F.R.S. in the Chair.

JAMES GLAISHER, Esq. F.R.S.

On Scientific Experiments in Balloons.

In the introductory part of the discourse, Mr. Glaisher gave a brief history of aerostation, from the discovery of the fire-balloon in the year 1782, by the two brothers Montgolfier, noticing some of the principal ascents made with fire-balloons. He then spoke of the discovery of Cavendish in 1776, viz. that hydrogen gas was fully ten times lighter than common air; when it immediately occurred to Dr. Black, of Edinburgh, that if so, a thin bladder filled with this gas ought to rise of itself: yet a period of several years elapsed before this obvious property was applied to the inflation of balloons; not in fact till the success of the fire-balloon was established. He then spoke of the more remarkable ascents and experiments which were made with air-balloons within a few years of its discovery, and remarked, that the result of the several experiments having proved that the balloon would raise great weights in the air, and remain for a long time thus suspended, caused a general desire to navigate the lofty regions of the atmosphere, and to pursue meteorological and other investigations in those regions, and the invention of the balloon was looked upon as likely to be followed by great consequences. He then spoke of the different ascents which have been made in the interests of science: the first of which was that of Mr. Boulton, well known as the partner of the famous Watt, who constructed a balloon to which a match and serpent were attached, that the gas might explode in the air. The object was to determine whether the reverberating sound of thunder was caused by echo or by successive explosions; the point remained unsettled owing to the shouting of the people; but it was thought that the sound did resemble thunder.

This experiment was made on December 26, 1784. No further experiments were made, so far as he knew, till the beginning of the present century, when in the years 1803 and 1804, Mr. Robertson VOL. IV. (No. 38.)

F

made three ascents from St. Petersburg, for the purpose of making magnetical and other experiments.

On August 23, 1804, MM. Gay-Lussac and Biot ascended from Paris for a similar purpose; they attained an altitude of 13,000 feet, and found no difference in their experiments in electricity, magnetism, and galvanism from those made on the earth.

On September 15, Gay-Lussac ascended alone to a height of 22,977 feet; he found that the temperature declined from 82° to 15°; that the sky was deep blue; that the time of horizontal vibration of a magnet was shorter with elevation.

In 1806, Carlo Brioschi, Astronomer-Royal at Naples, endeavoured to ascend higher than Gay-Lussac; the balloon burst, but its remnant happily checked the rapidity of the descent.

A period of forty-four years followed, during which no systematic attempts were made to take scientific observations by means of balloons.

In 1850, MM. Bixio and Barral inflated a balloon with hydrogen gas, in the gardens of the Observatory at Paris, with the intention of ascending to a height of from 30,000 to 40,000 feet; in their first ascent they ascended to a height of 19,000 feet, and descended to the earth in 47 minutes; they passed through a mass of cloud 9000 feet in thickness.

In their second ascent, clouds were reached at 7000 or 8000 feet, which proved to be 15,000 feet in thickness; they never, in fact, passed out of the clouds; for when they were 23,000 feet high, they began to descend, owing to a rent in the balloon.

Mr. Welsh's experiments were made in the year 1852: on August 17 and 26, October 21, and November 10, the respective heights attained in these were 19,500 feet, 19,100 feet, 12,640 feet, and 22,930 feet: a great number of observations were made, from which the following law regarding the decline of temperature with elevation was deduced :

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"That the temperature of the air decreases uniformly with the height above the earth's surface, until at a certain elevation, varying on different days, the decrease is arrested, and for a space of 2000 or 3000 feet the temperature remains nearly constant, or even increases by a small amount: the regular diminution being afterwards resumed and generally maintained at a rate slightly less rapid than in the lower part of the atmosphere, and commencing from a higher temperature than would have existed but for the interruption noticed."

These results, as well as those found by Gay-Lussac relative to the decline of temperature with increase of elevation, appeared to confirm the law which theory, based upon observations upon mountain sides, assigns for the gradation of temperature; viz. a decrease of one degree of temperature for every increase of 300 feet. Up to the present time therefore the high expectations entertained on the discovery of the balloon have never been realized.

The speaker then proceeded to state, that since the formation of the British Association, grants of money have been made for the

purpose of pursuing these inquiries; but with the exception of those by Mr. Welsh, none have been made.

In the year 1861, another grant of money was made, and a committee appointed to carry out experiments by means of the balloon, and the task of making these experiments was undertaken by the speaker.

The primary objects of the experiments with which he was entrusted were :—

The determination of the temperature of the air and its hygrometrical states at different elevations up to five miles.

To compare the readings of an aneroid barometer with those of a mercurial barometer up to five miles.

To determine the electrical state of the air.

To determine the oxygenic state of the air by means of ozone papers.

To determine the time of vibration of a magnet on the earth, and at different distances from it.

To determine the temperature of the dew point by Daniell's Dew Point Hygrometer, Regnault's Condensing Hygrometer, and by the use of the Dry and Wet Bulb Thermometers as ordinarily used, and by their use when under the influence of the aspirator, so that considerable volumes of air are made to pass over their bulbs, at different elevations, as high as possible, but particularly up to those heights where man may be resident or where troops may be located, as in the high lands and plains of India, with the view of ascertaining what confidence may be placed in the use of the Dry and Wet Bulb Thermometers, by comparison with the results as found from them and with those found directly by Daniell's and Regnault's Hygrometers; and to compare the results as found from the two hygrometers together.

To collect air at different elevations.

To note the height and kind of clouds, their density and thickness at different elevations.

To determine the rate and directions of different currents in the atmosphere.

To make observations on sound.

To note atmospherical phenomena in general, and to make general observations.

The speaker then described the method of managing a balloon, spoke briefly of the several ascents already made, and then proceeded to speak of some of the results.

Speaking of the ascent on July 17, the departure of the temperature from a regular progression was very remarkable. Below the cloud the decrease was nearly uniform; on passing above it there was an increase of 6°; the decrease was then resumed, and the temperature was 26° at 10,000 feet, and continued at this reading till 13,000 feet had been passed; a very remarkable increase then took place, and at 19,500 feet a temperature of 42° was registered, and then declined rapidly to 160 at five miles. In descending, a disturbance from a

regular increase was met with at 24,000 feet, and continued to 17,000 feet; at 13,000 feet clouds were reached and no observations were made below 10,000 feet.

The temperature of the dew point approached that of the air in the cloud but did not touch it, and then separated more and more until at the highest point there was almost an entire absence of moisture.

On August 18, the temperature of the air decreased as usual on leaving the ground, until at the height of 4000 feet the rapidity of the decrease was checked and a warm current of air was met with and continued to 11,500 feet; the balloon then descended and passed through the same warm current extending to the same limits, and again passed through it on its reascension at about the same height, and extending to 14,000 feet, when the regular diminution was resumed and continued to the highest point; on descending, the same warm current was met with, and continued till the clouds were entered at 6500 feet, which caused another interruption in the regular increase of temperature as is usual on entering cloud.

In the ascent on September 5, on passing out of the cloud there was an increase of temperature of 9°; and then no interruption was met with till a height of 15,500 feet was reached, when a warm current of air was reached, and continued to 24,000 feet: then a regular decrease was experienced till the highest point was reached.

On descending, the same warm current was encountered between 22,000 and 23,000 feet; and a similar interruption, but to a greater amount, was experienced till the balloon had descended to about the same height as it was first met with on ascending. After this there was no further interruption till the descent was completed.

A table was then formed from all the observations, showing the decrease of temperature for successive increases of elevation of 1000 feet. The results are as follows:

From these results it will be seen that when the sky is cloudy, the decline of temperature differs very little from the theory of a decline of temperature of 1° in 300 feet.

0 to 1000 was 7 2 from 5 experiments, or 1 in 139 1000 to 2000 was 5.3 from 5

Ft.

2000 to 3000 was 4.6 from 5

1 in 189

1 in 254

1 in 295

1 in 370