406 
presented in the form usual in the several branches of trade sta- 
tistics. The result is that the values stated for the different pro- 
ducts are necessarily taken at different stages of production or 
transportation, &c. Theoretically perfect statistics of mineral 
products would include first of all the actual net spot value of 
each substance in its crudest form, as taken from the earth ; and 
yet for practical purposes such statistics would have little interest 
other than the fact that the items could be combined in a grand 
total in which each substance should be rated on a fairly even 
basis. The following groupings, therefore, are presented with 
a full realisation of the incongruity of many of the items. The 
grand total might be considerably reduced by substituting the 
value of the iron ore mined for that of the pig iron made, by 
deducting the discount on silver, and by considering lime, salt, 
cement, borax, &c., as manufactures. It will also be remarked 
that the spot values of copper, lead, zinc, and chrome iron ore 
are much less than their respective values after transportation to 
market. Still the form adopted seems to be the only one which 
admits of a comparison of the total values of the mineral products 
from year to year. 
Résumé of the Values of the Metallic and Non-metallic Mineral 
Substances produced in the United States in 1884. 
Metals sia ads aa ts $186,097,599 
Mineral Substances named in the foregoing 
Table 220,007,021 
406, 104,620 
Fire-clay, kaolin, potter’s clay, common brick clay, 
terra cotta, building sand, glass sand, limestone 
used as flux in lead smelting, limestone in glass 
making, iron ore used as flux in lead smelting, 
marls (other than New Jersey), gypsum, tin ore, 
antimony, iridosmine, mill-buhrstone, and stone 
for making grindstones, novaculite, corundum, 
lithographic stone, tale and soapstone, quartz, 
fluorspar, nitrate of soda, carbonate of soda, 
sulphate of soda, native alum, ozokerite, mineral 
soap, strontia, infusorial earth and tripoli, pumice- 
stone, sienna, umber, &c., certainly not less than 7,000,000 
Grand Total a fe --  $413,;104,620 
The total value of the metals and minerals produced in 1884 
was $39,100,008 less than in 1883, and the decline in 1883 from 
1882 was $3,012,061 ; that is, the falling off in value began on 
a small scale in 1883, but was accentuated in 1884. The 
net decline has been due rather to a depression in price than 
a decrease in quantity; indeed, several important substances 
show a decided increase in production, notwithstanding the 
general dullness of trade. The over-production, taking the 
whole field into consideration, has been less than was generally 
feared. 
PROF. L. SOHNCKE ON THE ORIGIN OF 
THUNDERSTORM ELECTRICITY } 
[XN order to express more than mere surmises as to the origin 
of thunderstorm electricity we must, above all, be familiar 
with the atmospherical conditions under which thunderstorms 
usually occur, For this purpose we must first take into con- 
sideration two general facis in meteorology : first, the average 
decrease of temperature with increase of height in free air; and 
secondly, the nature of the upper clouds. 
With regard to the first point, a considerable amount of data 
is available in the observations of several scientific balloonists, 
especially those of Mr. J. Glaisher. Glaisher has constructed a 
table, based upon his numerous ascents, showing the average 
decrease of temperature for the altitudes of 1000, 2000, 3000 
feet, &c. This table shows that even in the warm summer 
months the temperature of the freezing-point is met with gener- 
rally at the level of between 3000 and 4000 metres (say 10,000 
to 13,000 feet). 
Generally speaking, the aggregate of those points of space in 
which the temperature of 0° C, prevails at any given moment must 
lie on a certain surface, which may be denoted as the ‘‘isother- 
mal surface of zero C.” It is of especial interest to ascertain 
whether the result yielded by Glaisher’s ascents as to the height 
* Extract from ‘‘ Sitzungsberichte der Jenaischen Gesellschaft fiir Medecin 
und Naturwissenschaft.” Jahrg. 1885. Sitzung vom 1 Mai. 
NA TORE 
[August 27, 1885 
of this surface in midsummer is confirmed by other ascents. In 
order to obtain an opinion upon this point I have grouped toge- 
ther those ascents which afford a sufficient number of data, in 
order to deduce therefrom the height of the isothermal surface 
of zero. This table includes twenty-three ascents by eight diff- 
erent balloonists at different seasons of the year ; about half the 
ascents were made during the summer months. The following 
are the conclusions drawn from this table :— 
In the warmest summer months the isothermal surface of zero 
was found to be at an height of about 3000 to 4000 metres, but 
occasionally sinks even at this season to about 2000 metres (say 
6500 feet) above the level of the sea. It generally rises in the 
course of the forenoon, and, apparently, more rapidly the nearer 
noon is approached. It sinks inthe course of the afternoon, and, 
apparently, more rapidly with the greater distance from noon. 
Its level may vary about 2000 metres in from one to two hours. 
The change from rising to sinking does not occur cxactly at 
noon, but perhaps one hour or even more after noon, according 
to season. 
A knowledge of the decrease of temperature on days of 
thunderstorms, especially just befure the storm, presents therefore 
especial interest. Only few data exist on this point. 
Glaisher made an ascent at 6 p.m. on the 31st August, 1863, 
after a thunderstorm had taken place at 8a.m. He did not 
reach the isothermal surface of zero, but found a temperature of 
1° C. at a height of 2300 metres (say 7500 feet). I have never 
found such a low ternperature at a similar height in any of the 
six ascents in August and the beginning of September. 
Flammarion made an ascent during the night of the thunder- 
storm of the 14-15 July, 1868, and met witho® C. at a height of 
2400 metres (say 6500 feet), but this was at 4h. 26m. a.m. 
Among all the midsummer ascents there is only one in which the 
isothermal surface of zero was met with at a lower level. 
Welsh made an ascent in the afternoon of the 17th August, 
1852, two hours before the occurrence of a thunderstorm; at 
5 p.m. the isothermal surface of zero lay at a height of -3500 
metres (say 11,500 feet), but it was rapidly sinking. Welsh did 
not find such a rapid decrease of temperature upwards in any of 
his other three ascents as in this one. 
Kamtz has drawn the conclusion, based upon the great refrac- 
tion which has often been observed with sultry thunderstorm air, 
that the rapid change of temperature with height is an important 
condition for the formation of thunderstorms, especially in 
summer. In order to obtain more precise data upon this point 
I have undertaken a small meteorological investigation as to the 
difference of temperature existing just before thunderstorms 
between Freiburg in the Breisgau and the Héchenschwand in the 
Black Forest, 2326 feet above it. I found that inseventeen cases 
which were suitable for comparison, in the years 1880 and 1881, 
the difference of temperature just before the thunderstorm was 
less than the average for the day and season in three cases only ; 
in other cases it was greater. 
From this it appears that, in most cases, the abnormally rapid 
decrease of temperature with height, and, in connection with this, 
the abnormally low position of the isothermal surface of zero 
may be taken as characteristic of the condition of weather before 
thunderstorms. 
Secondly, attention must be paid to the nature of the upper 
clouds not only generally, but also more especially before 
thunderstorms. The clouds which lie above the isothermal sur- 
face of zero must of course mainly consist of ice particles, 
although, of course, the formation of clouds of superfused water 
particles is not excluded. The appearance of the ice clouds is, 
moreover, somewhat different from that of the water clouds. 
The former are known as ‘‘ cirrus” and the latter as ‘* cumulus ” 
clouds. Observations on the height of clouds, made either in 
balloon ascents or on the ground, agree in showing that the 
limit of both kinds of clouds in midsummer lies about 4000 
metres (say 13,000 feet) high, which agrees pretty well with the 
above calculation of the level of the isothermal surface of zero. 
It is not surprising, therefore, that balloonists frequently reach 
snow-clouds even in midsummer—for instance, Glaisher on June 
26, 1863, between 3300 and 4200 metres (Say 11,000 and 14,000 
feet); Fonvielle on July 4, 1875, at 3450 metres (say I1,300 
feet) ; Barral and Bixio on July 27, 1850, between 4500 anil 
6300 metres (say 15,000 to 20,500 feet) ; Welsh on August 17, 
1850, at 5990 metres (say 19,500 feet). 
While the distinction between ice and water-clouds, from their 
mere appearance as seen from the earth, is always somewhat diffi- 
cult to be made out, we have in many cases an infallible 
eae os Peli =< . 
