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SCIENCE. 



|Vol. VII. , No. 161 



be, there is no violation of the fundamental law of 

 modern physics, — no destruction of energy. 



The second practical problem is to cover as large 

 a surface as possible with the viscous fluid. Fortu- 

 nately this can be done easily in accordance with 

 principles explained in many modern treatises on 

 capillarity : for the surface tension of the film between 

 water and air is so much greater than the sum of 

 the tensions, oil water and oil-air, that a drop of oil 

 is very rapidly drawn out over an enormous surface. 

 If this paper were not already so long, some numeri- 

 cal data might be given. The preference shown for 

 animal or vegetable oils over mineral oils (Science. 

 vii. 133) is probably justified by the smaller surface 

 tension and greater viscosity of the former ; though 

 it may be noted, that, the greater the viscosity, the 

 slower the oil will spread, other things remaining the 

 same. 



To render complete the explanation of this inter- 

 esting and at first sieht puzzling action of oil, experi- 

 ments are needed by physicists in the laboratory, 

 where for various oils the several physical properties 

 above named shall be measured, aud also experiments 

 and observations at sea when wind and waves are 

 moderate enough to be measured, and the captain 

 may go in any desired direction without danger. A 

 few days' observations, where the conditions can be 

 controlled, would be worth hundreds of the desultory 

 reports which the hydrographic office is wisely col- 

 lecting. Charles K. Wead. 



Professor Thorell and the American Silurian 

 scorpion. 



Profpssor Thorell, who is perhaps the best authority 

 upon the Senrpionidae, both recent and fossil, has 

 rather severely taken to task some of my statements 

 and determinations in connection with the recently 

 discovered American Silurian scorpion (see American 

 naturalist for March, 1886, p. 269). In fact, so 

 sharp and puneent are some of his remarks, that a 

 person reading them would naturally infer, that, in 

 Professor Thorell's opinion, I was hardly capable of 

 making a reliable observation, at least not upon a 

 scorpion. He has shown his good nature, however, 

 in the outstart, by admitting that the specimen is 

 really a scorpion, and not a Eurypteroid, — a con- 

 clusion the exact contrary of that jumped to by one 

 critic upon reading the first announcement of its dis- 

 covery. For this concession Professor Thorell has 

 my heartiest thanks. In his further criticisms, how- 

 ever, he is much less lenient, and I wish to briefly 

 notice his objections in their order. 



After making the above-mentioned admission, Pro- 

 fessor Thorell proceeds to deal with the six ventral 

 plates of this, what he calls, ' rather badly preserved 

 fossil ' In my description in the American museum 

 bulletin, I mention that the specimen is ' greatly 

 compressed ; ' that the ' dorsal crust is preserved 

 over about two-thirds of the surface.' mentioning 

 the parts; and that "over the rest of the prae-ab- 

 domen and what remains of the post-abdomen or 

 tail, parts of the first five segments, the inside 

 of the ventral crust is exposed " This feature of 

 the specimen has, I fear, misled Professor Thorell, 

 and caused him to fall into an error, into which, if 

 he had known the nature of the preservation of the 

 fossils (Eurypteroids) found in the formations from 

 which the scorpion was obtained, he probably would 

 not have fallen. The specimen is greatly compressed 



vertically, as are all the fossils in the same rock. 

 Along the left side of the abdomen there is a line of 

 fracture, to the right of which the substance of 

 the dorsal plates, and the filling between them, to 

 the ventral plates below, has been removed in split- 

 ting the rock, and probably left on the other part. 

 Along this line the thickness between the two sides 

 of the fossil (dorsal and ventral) is about a twentieth 

 of an inch or less. In speaking of this feature, Pro- 

 fessor Thorell says, "The whole upper side of the 

 abdomen is broken or cracked longitudinally," and 

 that the articulations of the ventral parts are '"all 

 direct continuations of the articulations between the 

 dorsals." Neither of these assertions is entirely true. 

 The abdomen is partially removed, but not 4 cracked ' 

 in the sense in which he uses the term ; and the 

 articulations between the joints of the ventral plates 

 are not ' direct continuations ' of those of the dorsal. 

 Besides this, the overlapping of the plates show 

 directly which is dorsal, and which is ventral ; and 

 no zoologist would be apt to make the mistake. If 

 we examine the abdomen of a beetle, roach, or 

 scorpion, on the exterior, we find the anterior plates 

 all overlapping those behind, both dorsally and ven- 

 trally : but, if we take off the crust and examine the 

 inside, we find the reverse to be the case ; that is, 

 the anterior edge of the plates overlaps the one an- 

 terior to it. Now, this is precisely what is seen on 

 this specimen : on the left side the anterior plates 

 overlap those behind, while on the right side the 

 posterior overlap those in front ; and the surface of 

 the plates is concave, while on the left side they are 

 convex ; so that a mistake is nearly impossible. Pro- 

 fessor Thorell's statement, that, if his interpretation 

 of this character is the right one, "the want of 

 spiracles on the plates needs no further explanation," 

 is therefore of no value, as he reasons from false 

 premises : all his conclusions based upon his assumed 

 features fall to the ground, and the want of spiracles 

 is yet unexplained. There are six of these ventral 

 plates plainly seen, extending: from beneath the dor- 

 sals. Neither is the specimen a ' rather badly pre- 

 served fossil,' but instead an exceedingly well pre- 

 served and distinct one, as far as the parts existed 

 w 7 hen the specimen was embedded. 



In a footnote to bis observations on the above 

 structure, Prof essor Thorell states, that, "even if the 

 plates in question really were ventral plates, the first 

 (or sixth when counted from behind forward) would 

 seem, from its position, to correspond to the anterior 

 half of the first ventral in the ordinary scorpions, 

 and not to the small plate situated between the 

 pectoral combs." On this statement I will make no 

 comment, further than to say that I have failed to 

 find, in the living species which I have examined, 

 any case where the first (or anterior) ventral plate 

 is even apparently articulated to the third ventral 

 plate, or has the lateral width of this one. 



Professor Thorell next goes on to say that " Mr. 

 Whitfield thinks, that, whereas modern scofpions 

 carry the tail (post-abdomen) arched upward over 

 the back, Proscorpius, and also Palaeophonus, car 

 ried it in the opposite way. or curved downward." 

 He says, " This would indeed be a character of 

 fundamental importance for distinguishing the Silu- 

 rion scorpions from all other members of the group," 

 but that to him it is "impossible to find any strin- 

 gent reason for adopting this strange hypothesis," 

 and that it would cause "the animal's gait to be 

 exceedingly difficult and awkward if it were to walk 



