155 



SCIENTIFIC SIDE-LIGHTS 



fewer; in the rodent fewer still; in the dog 

 very few indeed; and in apes and men 

 hardly any at all. JAMES Psychology, vol. 

 i, ch. 2, p. 21. (H. H. & Co., 1899.) 



757. DELICACY OF ADJUSTMENT 



Rostellum of Orchid Set Like a Hair-trigger. 

 To show how delicate a touch suffices to 

 cause the rostellum [of the List era ovata] 

 to explode, I may mention that I found an 

 extremely minute hymenopterous insect 

 vainly struggling to escape, with its head 

 cemented by the hardened viscid matter to 

 the crest of the rostellum and to the tips 

 of the pollinia. The insect was not so large 

 as one of the pollinia, and after causing the 

 explosion had not strength enough to re- 

 move them; it was thus punished for at- 

 tempting a work beyond its strength, and 

 perished miserably. [A larger insect would 

 have carried away the adhering pollen to 

 drop it on the stigma of another flower.] 

 DARWIN Fertilisation of Orchids, ch. 4, p. 

 120. (A., 1898.) 



758. DELICACY OF ORGANIC 

 STRUCTURE Vibrations Caught by Eye and 

 Ear. All the organs of sense discharge 

 their functions in virtue of a purely me- 

 chanical adjustment between the structure 

 of the organ and the particular form of ex- 

 ternal force which it is intended to receive 

 and to transmit. How fine those adjust- 

 ments are can best be understood when we 

 remember that the retina of the eye is a 

 machine which measures and distinguishes 

 between vibrations which are now known to 

 differ from each other by only a few mil- 

 lionths of an inch. Yet this amount of dif- 

 ference is recorded and made instantly ap- 

 preciable in the sensations of color by the 

 adjusted mechanism of the eye.. Another 

 adjustment, precisely the same in principle, 

 between the vibrations of sound and the 

 structure of the ear, enables those vibrations 

 to be similarly distinguished in another 

 special form of the manifold language of 

 sensation. And so of all the other organs of 

 sense they all perform their work in virtue 

 of that purely mechanical adjustment which 

 places them in a given relation to certain 

 selected manifestations of external force, 

 and these they faithfully transmit, accord- 

 ing to a code of signals the nature of which 

 is one of the primary mysteries of life, but 

 the truthfulness of which is at the same 

 time one of the most certain of its facts. 

 ARGYLL Unity of Nature, p. 37. (Burt.) 



759. DELIVERER BECOMES A 

 SCOURGE The Pharaoh Rat : His Uses and 

 Abuses. A dozen years ago the rats multi- 

 plied superabundantly in the sugar planta- 

 tions of Jamaica, where they gnawed the 

 stalks, sucked the sap from the incision, and 

 as soon as they had determined the fall of 

 one cane abandoned it for another. This 

 manner of operating had entailed a consider- 

 able loss upon the planters, and they con- 

 cluded to exterminate the rats with energy. 

 For this purpose, . . . six ichneumons 



were imported from India (Herpestes ich- 

 neumon, or Pharoah's rat, a kind peculiar to 

 Egypt, Palestine, and Tunis ) . This species 

 is the hereditary enemy of rats and ser- 

 pents, so that, multiplying rapidly, they 

 soon cleared the devourers from the planta- 

 tions. The rats then invaded the farms and 

 the villages, but were pursued there also by 

 the ichneumons, destroying them as well as 

 their offspring in the nests. ... As for 

 the ichneumons, so useful oji their arrival, 

 no longer having rats to devour, they then 

 began to turn up in the poultry-yards, where 

 they destroyed the eggs and young chickens ; 

 they have also totally exterminated the 

 quail and the partridge of the island, whose 

 eggs, deposited upon the ground, are an 

 easy prey. They empty the eggs by making 

 in each a tiny hole, and the ignorant mother 

 bird continues to cover the sterile eggs. The 

 Jamaicans, delivered from the rats by 

 Pharoah's rat, are now seeking a new animal 

 to deliver them from their deliverers. 

 Revue des Sciences Naturelles Appliquees, p. 

 960, 1890. (Translated for Scientific Side- 

 Lights.} 



76O. DELTA OF THE MISSISSIPPI, 

 ANTIQUITY OF Vast Time Required for 

 Deposition. When I visited New Orleans, 

 in February, 1846, I found that Dr. Eiddell 

 had made numerous experiments to ascer- 

 tain the proportion of sediment contained in 

 the waters of the Mississippi; and he con- 

 cluded that the mean annual amount of solid 

 matter was to the water as TTTTT * n weight, 

 or about ^Vrr ^ n volume. From the obser- 

 vations of the same gentleman, and those of 

 Dr. Carpenter and Mr. Forshey, . . . the 

 average width, depth, and velocity of the 

 Mississippi, and thence the mean annual dis- 

 charge of water, were deduced. I assumed 

 528 feet, or the tenth of a mile, as the 

 probable thickness of the deposit of mud and 

 sand in the delta; founding my conjecture 

 chiefly on\ the depth of the Gulf of Mexico, 

 between the southern point of Florida and 

 the Belize, which equals on an average 100 

 fathoms, and partly on some borings 600 

 feet deep in the delta, near Lake Pontchar- 

 train, north of New Orleans, in which the 

 bottom of the alluvial matter is said not to 

 have been reached. The area of the delta 

 being about 13,600 square statute miles, and 

 the quantity of solid matter annually 

 brought down by the river 3,702,758,400 

 cubic feet, it must have taken 67,000 years 

 for the formation of the whole; and if the 

 alluvial matter of the plain above be 264 

 feet deep, or half that of the delta, it must 

 have required 33,500 more years for its ac- 

 cumulation, even if its area be estimated as 

 only equal to that of the delta, whereas it is 

 in fact larger. If some deduction be made 

 from the time here stated, in consequence of 

 the effect of the driftwood, which must have 

 aided in filling up more rapidly the space 

 above alluded to, a far more important al- 

 lowance must be made, on the other hand, 

 for the loss of matter, owing to the finer 



