In the following table I have entered in the first column the names of the peaks ascended by Mr. Whymper; in the second, the height of each as given by him; in the third, the observed temperature in degrees Centigrade; in the fourth, the difference between the observed temperature and 27° C.—that assumed for Guayaquil; in the fifth, the average number of metres corresponding to a fall of 1° C. in rising from the sea-level to the higher station; in the sixth, the difference between the observed temperatures and that assumed for Quito—14·4°; and in the seventh, the average number of metres corresponding to a fall of 1° C. in rising from Quito to the higher station. It is obvious that the more rapid the fall the less will be the number in columns 5 and 7.
| Name of Mountain. | Height above sea-level. | Observed temperature. | Difference of temperature at sea-level. | Average number of metres for fall of 1° C. from sea-level. | Difference of temperature at Quito. | Average number of metres for fall of 1° C. from Quito. | |
|---|---|---|---|---|---|---|---|
| 1 | Chimborazo (Jan.) | 6253 | -6·1 | 33·1 | 189 | 20·5 | 166 |
| 2 | Chimborazo (July) | 6253 | -8·06 | 35·06 | 178 | 22·46 | 151 |
| 3 | Mean of (1) and (2) | 6253 | -7·08 | 34·08 | 183·5 | 21·48 | 158·5 |
| 4 | Cotopaxi | 5959 | -8·4 | 35·4 | 168 | 22·8 | 136·5 |
| 5 | Antisana | 5870 | +11·1 | 15·9 | 369 | 3·3 | 916 |
| 6 | Cayambe | 5852 | +2·5 | 24·5 | 239 | 11·9 | 252 |
| 7 | Cahihuairazo | 5035 | +4·44 | 22·56 | 223 | 9·96 | 220 |
| 8 | Cotocachi | 4965 | +2·2 | 24·8 | 202 | 12·2 | 173·5 |
| 9 | Pichincha | 4851 | +7·77 | 19·23 | 255 | 6·63 | 302 |
| 10 | Corazon | 4837 | +4·44 | 22·56 | 214 | 9·96 | 200 |
| 11 | Sara Urcu | 4718 | +10·0 | 17·00 | 284 | 4·4 | 425 |
It will at once be seen that the temperatures observed on Antisana, Pichincha, and Sara Urcu were altogether exceptional, probably due to rapid condensation of vapour; and these may best be excluded from any discussion of the general results. The temperatures noted in the second ascent of Chimborazo were probably below the mean, or at least below the mean for the hours at which most of the other observations were made. But, as opinions may differ on that point, I have also given below the results of comparison with the mean for the two ascents of Chimborazo. For a similar reason I regard the figures for Cotopaxi, where Mr. Whymper remained for twenty-six hours on the summit, as giving too low a temperature, while that observed on Cayambe is certainly too high. The mean result for these two summits is probably a near approximation to the average for that height.
In attempting to draw conclusions from the above table, we must first remark that, in consequence of its position on a plateau, the temperature of Quito is considerably higher than it would probably be if the higher peaks descended with an uniform slope to the sea-level. The difference between the means for that place and Guayaquil is only 12·6° C.; whereas, on the supposition of an uniform decrease in ascending from the sea-level, it should be 14·2°, and still greater if we supposed that the rate of fall of temperature gradually diminishes as the elevation increases. Omitting altogether the results for numbers 5, 9, and 11 in the above table, we perceive that the observations fall into three groups: (1) those for Chimborazo, at 6253 metres; (2) those for Cotopaxi and Cayambe, with a mean height of 5905 metres; (3) those for Cahihuairazo, Cotocachi, and Corazon, whose mean height is 4950 metres. To these it may be well to compare the mean of the results for the entire series, and also the rate of decrease between the sea-level and Quito. I shall designate observations included hereunder by numbers corresponding to the lines in the preceding table. The number of metres of ascent corresponding to a fall of 1° C. gives the most convenient measure of the rate of decrease.
| Mean height. | Difference of temperature at sea-level. | Metres for fall of 1° C. from sea-level. | Difference of temperature at Quito. | Metres for fall of 1° C. from Quito. | |
|---|---|---|---|---|---|
| Quito | 2848 | 12·6 | 226 | 0 | 0 |
| Mean of 1, 4, 6, 7, 8, and 10 | 5483·5 | 27·19 | 201·5 | 14·59 | 180·6 |
| ” 3, 4, 6, 7, 8, and 10 | 5483·5 | 27·35 | 200·5 | 14·75 | 178·7 |
| ” 7, 8, and 10 | 4946 | 23·37 | 212 | 10·77 | 195 |
| ” 4 and 6 | 5905 | 29·95 | 197 | 17·35 | 176 |
We see from this table that, in ascending from the coast to the highest peaks of Ecuador, the average fall of the thermometer was, in round numbers, 1° C. for every 200 metres of ascent, while in ascending from the sea-level to the plateau of Quito the fall was proportionately less, being at the rate of 1° C. for 226 metres. On the other hand, the fall of temperature was more rapid in ascending from Quito to the higher peaks. On an average of all the ascents, we may reckon the rate of 1° for 180 metres. But it is remarkable that, taking the average of the three peaks which rise about 2000 metres above the level of Quito, the temperature fell only at the rate of 1° for 195 metres, while in ascending to peaks higher by nearly 1000 metres, the rate of fall was 1° for 176 metres, and if we take the still higher summit of Chimborazo we may reckon the rate of fall at about 1° for 160 metres.
The apparent increase in the rate of decline of temperature in the higher region is still more clearly shown if we compare the mean of the three peaks whose average height is 4946 metres, with that of the two whose average height is 5905. For a difference in the mean height of 959 metres, we find an average fall of 6·58° C., or a fall of 1° for 145 metres. Taking the first ascent of Chimborazo as giving the most probable results, we find that between this peak and the mean of the three lower summits, with a difference in height of 1307 metres, the difference of temperature is 9·73°, or a fall of 1° for 134 metres. Again, comparing Chimborazo with the mean of Cotopaxi and Cayambe, we find, for a difference of height of 348 metres, a difference of temperature of 3·15°, or a fall of 1° for 110 metres.
I am fully aware that these observations are not numerous enough to lead to any safe general conclusions; the comparatively high temperatures found at the height of about 5000 metres may be due to exceptional local conditions, such, for instance, as the ordinary formation of clouds at about that level; but, so far as they go, the observations tend to negative the supposition that in the tropics the rate of decrease of temperature diminishes as we ascend to the higher regions of the atmosphere.
MM. Reiss and Stubel made numerous observations in the Andes of Ecuador and Peru, during a prolonged visit to that region. Lists of heights obtained by reduction from their observations have appeared in various German scientific periodicals, and more fully in the American Journal of Science, vol. ii. pp. 268, 269; but, so far as I can ascertain, the record of their observations of the barometer and thermometer has never been given to the world.
In “Copernicus,” vol. iii. p. 193, et seq., Mr. Ralph Copeland has published a summary of the results of a series of meteorological observations made by him at various stations on the line of railway connecting Mollendo on the Pacific coast with Puno in Bolivia, near the lake of Titicaca, and also at La Paz and at Tacna. Two series of observations were made at Vincocaya, the summit station of the railway, 4377 metres above the sea. All the other stations are either on elevated plateaux, or on open slopes inclining gently towards the coast. The temperatures are partly derived from numerous observations and partly by taking the mean of the maxima and minima, with corrections for each station, the reasons for which are assigned by Mr. Copeland. In most of these I am inclined to concur, but there are two from which I am forced to dissent. In reducing Mr. Copeland’s tables to metrical measure, I have therefore ventured to make some corrections, which do not, however, much alter the results.