60 



KNOWLEDGE, 



[March 1, 1895. 



pberic electricity are similar, and their simultaneous study 

 will be useful to both." '' 



Against this general view Mr. Evershed argues that it 

 necessitates on the sun a continuous discharge of electricity 

 over the whole sphere, and that on the earth the 

 difference of potential does not imply a necessarily similar 

 discharge. The objection is only an apparent one, and 

 rests on the use of the word " discharge," which is not ap- 

 propriate in the case of the earth ; for in our air, which is 

 imperfectly isolating, we have simply in the ordinary case a 

 continuous outflow of electricity in the vertical direction ; a 

 greater difference of potential being necessai-y to form a 

 true discharge, as in the sun. The causes of the two 

 phenomena are the same, and act continuously so as to 

 maintain the ordinary state of things ; they have only 

 different intensities and effects. 



Likewise, when a body has a relatively feeble charge of 

 electricity, it loses its charge continuously and slowly in 

 the air, without any sensible effect on our senses ; it is 

 the ordinary case of our atmospheric electricity. If the 

 charge is greater, we can perceive in a dark room a feeble 

 blue hght around the body ; and with a much greater 

 potential the true discharge appears, attended by noise and 

 strong light. This is the case of the sun, where the high 

 temperature of the gases makes the discharge easier. 



The analogy between the two atmospheres appears to me 

 to be striking, and I have purposely refrained from seeking 

 the exact cause which maintains the differences of poten- 

 tial, because it is not useful for the comparison. 



3rd. AppUcaiion to the Stars and Nebula. — This analogy 

 can be extended up to a certain point to the other celestial 

 bodies, for in the spectrum of the sun, examined as a star, 

 the whole chromosphere is exactly represented by a feeble 

 bright line in the middle of the broad black line of calcium. 

 The sun, then, is a bright-line star, and may be grouped 

 with the variable stars, temporary stars, and nebulae. But 

 the bright line of the sun is very feeble relatively to the 

 continuous spectrum, whilst it is strong enough in variable 

 and temporary stars, where it was first discovered, and in 

 nebulse it is very strong indeed. On the other hand, the 

 line is reversed in the sun, but certainly has not the same 

 character in all the other bright-line stars, as Father 

 Sidgreaves has already noticed with the variable star 

 13 Lyrffi. I will examine only the case of the new star in 

 Auriga, which was formed, at the beginning, by at least 

 two bodies moving rapidly the one towards the other ; then 

 the bright lines of one of the bodies were very probably 

 reversed Unes, as recent studies on the corresponding line 

 of the sun have shown ; so that we are driven to see some 

 connection between the atmospheric electricity of the earth 

 and the singular case of the new star in Auriga. In fact, 

 the phenomenon of the new star is due either to the rapid 

 approach of two bodies or to a motion of matter, just as 

 atmospheric electricity, likewise, has often been ascribed to 

 the relative motions of the higher parts of our atmosphere. 

 Perhaps it may be possible to explain by some general 

 cause, very probably electrical also, all the gaseous lights 

 of the heavens — meteors, comets, the luminous atmospheres 

 of stars with their periodic variations, and nebulfe. 



Faithfully yours, 

 Paris Observatory. H. Deslandres. 



MECHANICAL FLIGHT. 

 To the Editor of Knowledge. 

 gm^ — One of the readers of Knowledge wishes to know 

 how I obtained by experiment, in 1875, a lifting force of 



* If we extend the analogy, we are driven to suppose in tlie atmos- 

 phere of the eartli a phenomenon similar to the solar corona. 



forty pounds per horse power, while Mr. Maxim only 

 obtained a thrust of two thousand pounds with three 

 hundred and twenty horse power, equal to only five and a 

 half pounds per horse power. As the subject may be 

 interesting to many of your readers, I venture to reply 

 through your columns. 



Not having been able to make a second travelling ex- 

 periment with my machine, through its accidental damage 

 by exposure to a heavy gale of wind, I fitted the engine 

 with two horizontal screws, as shown in the diagram, 



which is a plan view drawn 

 to a scale of a sixteenth of 

 an inch to the foot. The 

 screws were twelve feet in 

 diameter, arranged on each 

 side of the engine and boiler. 

 Twelve planes, each having 

 an area of seven square feet, were mounted on each 

 wheel. The hoops were formed of laminated pine, with 

 wire spokes, like velocipede wheels. The planes were made 

 of strong calico, mounted on bamboo canes, and, when 

 driven at full speed, the planes bellied to some extent, 

 thus acting as screw blades with increasing pitch. 



The screws were driven at sixty-seven revolutions per 

 minute, which would impart a speed of the effective 

 diameter of over twenty-three miles an hour. 



It would scarcely surprise anyone if a plane of one 

 hundred and sixty-eight square feet, driven in a straight 

 line at twenty-three miles an hour, were to sustain one 

 hundred and twenty pounds. Therefore it is not surprising 

 to me that fifty-six square feet to each horse power should 

 sustain forty pounds in my experiment. As it was made 

 twenty years ago, I cannot now remember the pitch of the 

 screws. 



Mr. Maxim's screws are seventeen feet ten inches in 

 diameter, and five feet wide at their ends. If these screws 

 were fitted to vertical axles, and not allowed to rise beyond 

 a few inches, as in my experiment, the effective surface 

 would be only thirty-six square inches to each horse 

 power. The difference is, therefore, in one case thirty-six 

 square inches, and in the other fifty-six square feet to each 

 horse power, and therefore my experiment naturally shows 

 nearly eight times the thrust of Mr. Maxim's screws, per 

 horse power. It is, however, necessary to bear in mind 

 that Mr. Maxim's screws were travelhng, while mine used 

 the whole power in slip. 



Not ha\dng any definite data as to the revolutions per 

 minute of Mr. Maxim's screws, I therefore cannot carry 

 the comparison further. 



Yours truly, 

 8, Quahty Comt, W.C. Thomas Moy. 



12th February, 1895. 



THE INTELLIGENCE OF INSECTS IN RELATION 

 TO FLOWERS. 



By the Rev. Alex. S. Wilson, M.A., B.Sc. 



BESIDES the attractions which they offer to insects, 

 flowers are generally provided with the means of 

 excluding certain classes of visitors. Diligent 

 visitors, as a rule, are welcome, and indolent 

 habits alone, as was shown in an article on the 

 "Industry of Insects in relation to Flowers" in the 

 December number of Knowledge, are suflicient to render 

 a visitor undesirable. The value of any set of fertilizing 

 agents depends on the number of separate flowers which 

 each individual visits ; multiplying the visitors does not, 



