96 Queries and Answers. 
That I have always considered uniformity in the manner in which observ- 
ations should be made by meteorologists, not only with respect to time, but 
as regards instruments of similar construction, of the greatest importance, 
I need only refer to a letter written by me, in Febr uary, 1823 (see Monthly 
Magazine, ‘vol. lv. p- 207.), recommending the establishment of a Meteorolo- 
gical Society in the metropolis ; and I should be most happy, at any time, to 
assist in the arrangement of some plan by which that desirable object could 
be obtained. 
I will now proceed, without further preface, to state the method practised 
by me in making my observations. The thermometer and barometer are 
examined eyery day at 8a.M., 3 P.M. (esteemed the hottest period of the 
day), and 10 p. m., and the extreme of cold is ascertained by a self-register- 
ing thermometer; thus giving four observations of that instrument, “all of 
which are duly registered, and the monthly mean is found by dividing the sum 
of all these by the number of observations, which, of course, varies with the 
number of days i in each month. The rain and evaporation are measured 
every morning at 8 o’clock, and the wind reported, if the prevailing wind of 
the day. From this statement, Mr. Gorrie will see that “ I refer to the 
daily extremes.’ The annual mean results fr om the division of the sum of 
the “monthly means by 12, or is the mean of means. If the averages of the 
monthly extremes had been alone attended to, the annual mean for the last 
year would have been lower than even that recorded in my report, being 
only 47°6041. 
f subjoin the annual temperature for the last seven years, by which the 
similitude between the years 1826 and 1828, noticed by Mr. Gorrie, very 
evidently appears. It would be extremely gratifying to me, and, no doubt, 
equally to your other meteorological readers, if Mr. Gorrie would favour us 
with the course pursued by him, in making his observations, and it might 
prove conducive to the adoption of some regular plan of observation among 
meteorologists, at any rate among those who correspond with the Magazine 
of Natural History. 
Annual mean for 1822  46°51° 
1823 44°26 
1824 46°11 
1825 46°81] 
1826 47°37 
1827 46°25 
1828 47°75 
T remain, Sir, &c. — James G, Tatem. Wycombe, May 21. 1829, 
Vision over the Sea. — Sir, It is stated (Vol. II. p. 470.) that a person, 
under favourable circumstances, could see over the surface of the ocean to 
the extent of 150 miles. I would ask under what circumstances an object 
on the surface of the earth or sea would be visible at that distance ; as, from 
the convex form of the earth, it would require an elevation of nearly three 
miles to bring it to a level with the horizon, or within the line of vision, 
setting aside the aid of refraction. Perhaps the limit of vision is unknown, 
the distance at which a body may be seen appearing to depend upon its 
size, the intensity of its light, and the state of the medium througli which 
the rays pass from it to the eye; as the planets, though too remote : for their 
figure to be discerned by the unassisted eye, are yet conspicuous from the light 
which they reflect ; whereas the fixed stars, from their immense distance, 
would be totally invisible to us, if, like the planets, they shone only by re- 
flected light. Perhaps some correspondent may furnish some useful inform- 
ation on the subject, and oblige, among others, your obedient servant, — 
I’. E. Southwark, Dec. 4, 1829. 
