TRANSACTIONS OF THE SECTIONS. 21 
in England—that send me their observations. Generally they arrive too late; and 
therefore they throw very little light on the forecasting”. ..... The author 
remarked that, for the future, “the normal heights of barometric pressure, or, 
better, of the barometers which are read, must be conscientiously taken; the 
observation must be made at more points once a day, and mutually communicated ; 
and at days when there are greatly different departures—that is to say, of three 
millimetres—or when there is change of inclination, there must be sent a message 
at noon or in the evening of the same day. In all cases, not only the pressure in 
the morning, but likewise that at night should be given. A critical indication is 
when on the previous day the northern stations had greater departures, and on the 
following day the southern had greater departures, even when the difference in the 
latter case was small. A caution should be given when the difference of the de- 
partures is four millimetres.” 
Description of an Instrument for ascertaining the Height of a Cloud. 
By Professor Curvattrer. 
This little instrument consists of two horizontal jointed rulers, graduated from 
the centre of the joint, the unit of graduation being the length of an upright sliding- 
piece, moveable upon either of the rulers. One branch of the rulers is directed to- 
wards the shadow of a cloud, the horizontal distance of which shadow from the 
place of observation can be ascertained ; and the other branch, carrying the vertical 
sliding-piece, is directed towards a vertical line drawn through the point of the 
cloud which casts the shadow. The sliding-piece being now moved along the ruler 
till the shadow of its inner edge just touches the inner edge of the other horizontal 
ruler, we have on the ruler and sliding-piece an exact miniature representation of 
the known horizontal distance of the shadow from the observer (s), and the height 
of the cloud (/) above the horizontal plane on which the shadow falls. 
Hence if d is the number of the divisions on the scale, and 1 the length of the 
sliding-piece, we have the proportion 
$i hei: ad: 1, 
whence 78 
d 
On the Path of a Meteorie Fireball relatively to the Earth’s Surface. 
By Professor Corrin, of Lafayette College, Eastern Pennsylvania. 
This meteor passed over the northern part of America on the 20th July, 1860, 
and was observed by different observers over a course of about 1000 miles. It 
was first seen at an elevation of 92 miles, then at 56 miles, and still lower after- 
wards at 39 miles. Its orbit appeared to be hyperbolic, and the paper described 
the various phenomena observed at the different stages of its progress until it 
traversed the distance of 500 miles over the sea. 
On Fogs. By J. H. Guapsronz, Ph.D., RS. 
The author had obtained additional returns of the occurrence of fog at different 
stations round the coasts of the United Kingdom; and on examining these with 
those previously brought before the notice of the British Association, he had been 
led to some new generalizations. The most important of these are— 
Ist. The distinction between general and local fogs.—A general fog is found to 
occur at every or almost every station along a whole country-side, extending 
usually one or two hundred miles, and often much more than that; while a local 
fog is marked at only one station, or perhaps at two very near together. There is 
nothing intermediate between these two kinds of fog; they do not pass insensibly 
one into the other; there is scarcely any record, in fact, of a fog visiting three or 
four stations and no more. Local fogs depend, no doubt, on peculiarities of the 
locality ; but it is difficult to draw just conclusions about them, as the peculiarities 
of the observer seriously affect the returns of them, and there is little or no check. 
A general fog, on the contrary, is at once recognized by the uniform occurrence of 
the same date in the lists, The fogs observed at the light-vessels at sea appear 
