228 



SCIENCE. 



[Vol. XXI. No. 534 



This accords with the result (3) already found for the mean 

 distance of the earth from the sun. In a paper on the " Intensity 

 of the Sun's Heat and Light" (Smithsonian Contributions to 



Knowledge, IX.), L. W. Meecli calls '"^ ^ " the sum of 



a-n t^ 1 _e2 



the intensities during a complete revolution." In this expression n 



is the mean daily motion and equals 1L. Substituting - for T 



T n 



and making /i equal to 1 in (4), the latter reduces to Meech's 

 formula. 



3. "If any two chords of the earth's orbit, as ^Xand BY, be 

 drawn through the sun, S, the amount of heat received in passing 

 over the arc AB equals the amount received in passing overXF." 

 (p. 83). Samuel Haughton ("New Researches on Sun-Heat," 

 1881) proves by another simple application of Kepler's second 

 law that the quantity of heat received by the earth in a given 

 time is proportional to the angle described in that time by the 

 radius-vector. For 



d6 — increment of true anomaly, 

 dt _dB 

 r' ~ 2 c 



This is but a mathematical translation of the argument given by 

 Herschel in "Outlines of Astronomy," 5th ed., § 368 b. The state- 

 ment made on page 82, "Cause of an Ice Age," is verified by an 

 employment of Haughton's expression. For since 



dh ex 



dt 



2c 



h <x 



2 c 



\ Now ASB = XSY = Sj -6^, 



and the proposition is established. The law that ' ' the amount of 

 heat received in any given interval is exactly proportional to the 

 true anomaly described in that interval" appears to have been 

 first published by Lambert in his " Pyrometrie," 1779. 



4. " The total heat received by the earth from equinox to equi- 

 nox is equal to that received while completing its journey around 

 the remaining part." (p. 83). The preceding demonstration does 

 not involve the inclination of the chords to each other, neither 

 does it involve the direction of either chord. Hence we may 

 make X coincide with B and Y with A, and let the one re- 

 sulting chord be the line of equinoxes, and the proposition 

 follows, 



5. "If 6 be the sun's declination the amounts of heat received 



by the Northern Hemisphei-e and the Southern are to each other 



as 1 -)- sin d to 1 — sin S." (p. 175). Draw a circle representing a 



section through the centre of the earth (regarded as a sphere). 



Let tlie horizontal diameter produced represent the celestial 



equator projected in a right line EE'. Through the centre of the 



circle draw AA', making an angle 6 with EE'. AA' will be the 



axis of the cylinder of heat-rays falling upon the earth when the 



sun's declination is 6. Draw a diameter, DD', perpendicular to 



AA', and at the upper extremity of DD' draw an element, TT', 



of the cylinder. To this draw a parallel, CC, intersecting EE' at 



the circumference of the circle. TT' and CC evidently include 



the portion of the cylinder falling on the Northern Hemisphere. 



If 2 iJ is the length of the diameter, the perpendicular distance 



2 H 

 between TT' and CC is seen to be iJ + Rsin S. Hence if . 



r/ 



be the quantity of sun-heat falling perpendicularly on an area 

 equal to the section of the earth at the mean distance r,, from the 

 R + Rsin A 2iT.._ 



sun in the unit of time. 



■(: 



2R 



') 



is the part falling 



on the Northern Hemisphere, while the remainder, ( ) 



^ ' V 2iJ / 



2H 



, falls on the Southern Hemisphere. 



2R 



These amounts are to 



each other as 1 -I- sin iJ to 1 — sin 6. 



One or two other propositions will be discussed in a subsequent 

 article. 



ON A PHYSIOLOGICAL CLASSIFICATION OF THE OPHIDIA 

 — WITH SPECIAL REFERENCE TO THE CONSTRICTIVE 

 HABIT. 



BT ARTHUR STRADLING, C.M.ZS., ETC., FLOKES, WALFOBD, HEET- 

 FORDSHIEE, ENGLAND. 



The writer would be the last to suggest a classification of 

 any group of animals whatsoever based upon physiological 

 data alone. Function, unless cortelated with definite variation 

 of structure, is never to be depended upon as a means of estab- 

 lishing specific differences. In illustration of this, one has only 

 to cite the numerous examples of change of function, not simply 

 within historic times, but even within the memory of living 

 man, owing to variation in the environment of the creatures 

 themselves. Witness the Kea, or New Zealand parrot, and the 

 baboon of South Africa, both of which have become carnivorous 

 since the introduction of sheep into this region; the bees of Eng- 

 land, which, in certain districts, have within the last twenty 

 years become frugivorous; and certain colonies of bats, inhabit- 

 ing the islands of the Gulf of Paria in Trinidad, which have of 

 late years taken to fishing, and have in consequence abandoned 

 their nocturnal habits, and are now strictly diurnal beasts of 

 prey. It is true that in certain isolated cases a change of func- 

 tion is followed by very slight variation of physical structure. 

 In that of the domestic cat the intestine has certainly become 

 elongated, and has probably undergone a further process of 

 elongation in consequence of its less purely carnivorous diet; in 

 particular, the duodenum has become more extended within recent 

 centuries, if one may judge from analogy when comparing the 

 creature with its vi'ild prototypes. 



In the case, however, of serpents, the family resolves itself 

 into three groups so naturally in accordance with the manner in 

 which they take their food, as to suggest the justification of a 

 natural grouping founded on this basis. 



If we had a specimen of every kind of snake before us, and 

 could watch them in the act of feeding, we should see that they 

 perform this process in three different manners. The majority, 

 numbering probably 1,000 or 1 300 out of the 1,800 known species, 

 simjjly catch the creatures on which they prey by the prehension 

 of their jaws and long curved teeth, and work them gradually 

 into the gullet on what we may call general principles. 



A great disproportion exists between the size of the captor and 

 of the captive. If the serpent be very much larger than the ani- 

 mal which it swallows, the latter is probably engulfed alive; but 

 it, as is commonly the case, the captive is of large diameter pro- 

 portionately to the oesophagus of the serpent, it is suffocated or 

 crushed to death in the act of swallowing. As may be expected, 

 the serpents that feed in this manner are such as live on what 

 may be termed soft food, — frogs, lizards, fish, or other snakes. 



But with the remainder we find two special provisions for the 

 slaughter of the prey previous to deglutition — provisions so re- 

 markable as to place the possessors in an entirely different cate- 

 gory to the preceding. In one of these, and by far the smaller 

 of the two subdivisions, numbering probably not more than 220 

 species altogether, or about one-eighth of the whole number of 

 snakes, we find the death of the prey is encompassed by the in- 

 jection of a morbific Quid, the venom. That this in the majority 

 of cases serves as ammunition for the destruction of the captive 

 cannot be doubted ; but whether this is the primary reason why 

 these creatures are gifted with venom is not so certain, seeing 

 that in many species it probably comes very little into play for 

 this purpose — e. g., in the sea snakes, in which the fangs are so 

 short that the fish on which they live are scarcely scratched by 

 them, and even in the great Ophiophagiis, the snake-eating snake 

 of India, whose natural diet consists of animals in which the 

 circulation is so slow and vitality so sluggish as serpents that they 

 are certainly swallowed before any poison could have time to 

 work its effect upon them. In all probability the primary office 

 of this remarkable fluid is to act as a digestive, it having been 

 found by experiment that albumen, pieces of hard-boiled egg, 

 etc., dissolve in this quite as readily as in the gastric juice of 

 any flesh-eating animal. The writer has further established by 

 his own experiments that small animals which have been sub- 



