NOVEMBER 20TH. An eclipse of the sun, which I had anxiously hoped to observe with a view of determining the longitude, happened this morning, and, as often took place in this cloudy climate, the sun was covered four minutes before it began. When it shone forth the eclipse was in progress, and a few minutes before it should (according to my calculations) have ended the sun was again completely obscured. The greatest patience and perseverance are required, if one wishes to ascertain his position when it is the rainy season.
Before leaving, I had an opportunity of observing a curious insect, which inhabits trees of the fig family ('Ficus'), upward of twenty species of which are found here. Seven or eight of them cluster round a spot on one of the smaller branches, and there keep up a constant distillation of a clear fluid, which, dropping to the ground, forms a little puddle below. If a vessel is placed under them in the evening, it contains three or four pints of fluid in the morning. The natives say that, if a drop falls into the eyes, it causes inflammation of these organs. To the question whence is this fluid derived, the people reply that the insects suck it out of the tree, and our own naturalists give the same answer. I have never seen an orifice, and it is scarcely possible that the tree can yield so much. A similar but much smaller homopterous insect, of the family 'Cercopidae', is known in England as the frog-hopper ('Aphrophora spumaria'), when full grown and furnished with wings, but while still in the pupa state it is called "Cuckoo-spit", from the mass of froth in which it envelops itself. The circulation of sap in plants in our climate, especially of the graminaceae, is not quick enough to yield much moisture. The African species is five or six times the size of the English. In the case of branches of the fig-tree, the point the insects congregate on is soon marked by a number of incipient roots, such as are thrown out when a cutting is inserted in the ground for the purpose of starting another tree. I believe that both the English and African insects belong to the same family, and differ only in size, and that the chief part of the moisture is derived from the atmosphere. I leave it for naturalists to explain how these little creatures distill both by night and day as much water as they please, and are more independent than her majesty's steam-ships, with their apparatus for condensing steam; for, without coal, their abundant supplies of sea-water are of no avail. I tried the following experiment: Finding a colony of these insects busily distilling on a branch of the 'Ricinus communis', or castor-oil plant, I denuded about 20 inches of the bark on the tree side of the insects, and scraped away the inner bark, so as to destroy all the ascending vessels. I also cut a hole in the side of the branch, reaching to the middle, and then cut out the pith and internal vessels. The distillation was then going on at the rate of one drop each 67 seconds, or about 2 ounces 5-1/2 drams in 24 hours. Next morning the distillation, so far from being affected by the attempt to stop the supplies, supposing they had come up through the branch from the tree, was increased to a drop every 5 seconds, or 12 drops per minute, making 1 pint (16 ounces) in every 24 hours. I then cut the branch so much that, during the day, it broke; but they still went on at the rate of a drop every 5 seconds, while another colony on a branch of the same tree gave a drop every 17 seconds only, or at the rate of about 10 ounces 4-4/5 drams in 24 hours. I finally cut off the branch; but this was too much for their patience, for they immediately decamped, as insects will do from either a dead branch or a dead animal, which Indian hunters soon know, when they sit down on a recently-killed bear. The presence of greater moisture in the air increased the power of these distillers: the period of greatest activity was in the morning, when the air and every thing else was charged with dew.
Having but one day left for experiment, I found again that another colony on a branch denuded in the same way yielded a drop every 2 seconds, or 4 pints 10 ounces in 24 hours, while a colony on a branch untouched yielded a drop every 11 seconds, or 16 ounces 2-19/20 drams in 24 hours. I regretted somewhat the want of time to institute another experiment, namely, to cut a branch and place it in water, so as to keep it in life, and then observe if there was any diminution of the quantity of water in the vessel. This alone was wanting to make it certain that they draw water from the atmosphere. I imagine that they have some power of which we are not aware, besides that nervous influence which causes constant motion to our own involuntary muscles, the power of life-long action without fatigue. The reader will remember, in connection with this insect, the case of the ants already mentioned.