226 



SCIENCE. 



[Vol XIII. No. 320 



ever, the question is the somewhat simpler one of determining the 

 conditions under which a bird can gain elevation without expend- 

 ing energy, velocities relative to the earth may, of course, be 

 ignored. 



There is, as I now see, a great advantage in making the simpler 

 investigation first : for, as Dr. Kimball has clearly shown, as 

 soon as we recognize the fact that the bird's motion relative to the 

 medium depends only on their relative velocity, it becomes clear 

 that gain of elevation, and consequently the whole phenomenon of 

 soaring, is impossible in a uniform horizontal wind. 



It follows that there was an error in my theory of soaring. Mr. 

 Gilbert thinks it due in part to my assuming it to be possible for a 

 bird to glide in a wind moving faster than itself, with its head to 

 leeward ; but I see no reason why birds should not accomplish this 

 fact, and am satisfied that I have often seen them do it. He also 

 holds that my bird, " in passing from a negative velocity relative 

 to the air, to a positive velocity relative to the air, must pass 

 through the phase of no velocity relative to the air, in which he is 

 practically helpless." But I was dealing with the bird's component 

 velocity in the line of the wind's motion ; and he might always 

 have a velocity relative to the air, though its component in that 

 line might be zero. The error which I made was in assuming, 

 that, under the conditions of flight to which I subjected my bird, 

 the turn to leeward was possible. From the way in which I made 

 him fly, it is clear that the resultant force exerted on him, at every 

 point of his supposed path, must be upward and to leeward. That 

 being the case, the turn to leeward could not be accomplished, 

 and consequently the path he was supposed to describe was an 

 impossible path. 



I feel that 1 must apologize to those of your readers who may 

 have followed me in what may fitly be called "a wild-goose chase." 



J. G. MacGregor. 



Dalhousie College, Halifax, N.S , March 8. 



" Shall We Teach Geology ? " 



In Professor Winchell's remarks on my review of his recent 

 work, there are only two points that call for reply. First, as to the 

 study of history, which, according to him, trains no faculty but 

 verbal memory. He now says that his " criticisms on history con- 

 template it as a study urged upon children in the early stages of 

 education," and that in the colleges it is pursued in a better way. 

 But, even if imperfectly taught, history trains far more important 

 faculties than verbal memory. It exercises the intellect generally 

 quite as much as geology does, and it also calls into play the moral 

 judgment and the sympathies, which geology does not. To Pro- 

 fessor Winchell the old red sandstone may be a more important 

 topic of study than the Roman Empire, and the plesiosaurus a 

 more interesting object of contemplation than Washington or 

 ■Columbus ; but to the mass of men this is not so. As to the time 

 that Professor Winchell would have spent on geology, I may have 

 misapprehended his meaning; and, if so, I am glad to be cor- 

 rected I haven't his book by me at present ; but, if I remember 

 rightly, he says that the study ought to be taken up in the primary 

 schools, and continited through the various grades, which I under- 

 stood to mean that the subject should be studied more or less every 

 year. He now says that he only wants it taken up several times at 

 intervals, and not pursued continuously, which is more moderate. 

 I do not see, however, how even so much study of geology is pos- 

 sible ; because, not to speak of languages and literature, there are 

 many sciences of greater importance than geology, which ought, 

 therefore, to be studied first. Such are arithmetic and geometry, 

 -geography, physics, human physiology, psychology, ethics, civil 

 polity, and history ; and I do not see how even all of these can be 

 taught in the public schools. If these views are correct, geology 

 ■can be nothijig but an optional study in the high schools and col- 

 leges, while in the lower schools it can have no proper place. 



The Reviewer. 



cordingly. As he pointed out, there are many ways in which the 

 principle of his method may be applied ; and I have lately thought 

 some instructive results might be obtained from examining sen- 

 tences with regard to length, as measured by the number of words. 



Length of sentences is a matter in which pronounced styles differ 

 greatly. Doubtless this is associated wi*h psychological peculiari- 

 ties which it might be instructive to inquire into. The mental 

 machine (so to speak) which, for example, turns out the long par- 

 enthetical sentences of Gladstone, must be very different in design 

 from that which yields the simple and direct utterances of John 

 Bright. 



I have made an examination of 300 sentences in each of the fol- 

 lowing works : Carlyle's " French Revolution," De Quincey's 

 " Confessions," and Johnson's " Rambler." The number of words 

 in each sentence was counted, and the sentences grouped accord- 

 ingly. Then the sentences with words up to 10 were added to- 

 gether, those with words from to to 20, from 20 to 30, and so on. 

 The accompanying curves were then obtained from these data. 

 Let it be clearly understood what they mean. The plain line 

 curve (for Carlyle) means that in the 300 sentences of the pas- 

 sage selected there were 62 containing words varying in number up 

 to 10, while 100 had from 10 to 20, and so on. The result is 

 roughly as we might expect : short sentences form the bulk of the 

 Carlyle passage, his maximum being in the class 10 to 20, and 

 sentences of more than 50 words are comparatively few. There 

 are none beyond 100. De Ouincey and Johnson, on the other 



AflD^ES OF STYLE FROM CARLYLE, DE QUINCEY, AND JOHNSON. 



Carlyle, heavy line ; De Quiticey, broken line ; Johnson, light line with dots. 



hand, have an abundance of longer sentences. De Quincey's most 

 numerous class is that of 20 to 30 words ; Johnson's, 30 to 40. But 

 the curve of the former does not die down till after no to 120 

 words (really there was one inordinate sentence of 170, not shown 

 in the diagram) ; while Johnson's is further protracted to 130 to 

 140. 



I do not affirm the constancy of these curves : they only apply 

 to the specified passages of 300 sentences. These few lines are 

 merely by way of suggestion, and should any reader have the time 

 and patience to pursue the inquiry further, he might, I think, find 

 his labors not without some useful results. 



It might be useful to see in what degree these curves approximate 

 to constancy, or come short of it. One would like to know better 

 than we do at present, how far the method, in any of its forms, is 

 reliable or helpful in settling disputed questions of authorship, or 

 in tracing anonymous literature to its source. 



I would suggest an examination of the words used by speakers 

 or writers as likely to be instructive. A. B. M. 



London, March 7. 



Curves of Literary Style. 



Tn the interesting researches on this subject by Professor Men- 

 denhall described in your journal in 1887, words were classified 

 •according to the number of letters in them, and curves made ac- 



Wind-Velocity and Wind-Pressure. 



From time to time there have appeared discussions of these 

 questions, so important to the practical engineer. It seems prob- 

 able that the first of these, as far as relates to the relation between 

 wind-movement and the travel of the cups of Robinson's anemom- 

 eter, is soon to be definitely settled by indubitable experiments. 



