SCIENCE. 



[Vol. XII. No. 283 



lowing the sinuosities of the bright streak ; then a dark band, par- 

 allel to, and following, every irregularity of the bright streak ; and 

 then nearly another eighth of an inch of ribbon-like light. In an- 

 other picture a very thin beaded flash has a precisely similar beaded 

 streak, rather fainter than itself, running parallel to it, at a distance 

 •of about a sixteenth of an inch on the paper. 



It might be suggested that the second fainter image was formed 

 by internal reflection from the back surface of the glass plate ; but 

 it should be noticed that sometimes very thin flashes, which are not 

 particularly bright, are so duplicated. 



A far more probable cause is the double image formed by the in- 

 ternal reflections of doublet photographic lenses. All doublets are 

 essentially two meniscus lenses, mounted with their concave sur- 

 faces facing one another. The greater portion of a strong point of 

 light, passing through both lenses, forms the usual image on the 

 plate ; but a smaller portion is reflected from the concave surface 

 •of the rear meniscus on to the concave surface of the front lens, 

 and from thence back through the rear lens to the sensitive plate. 

 The amount of displacement depends on the angle formed between 

 the direction of the bright point and the optical axis of the lens. 



M. C. Moussette of Paris showed some photographs of the sun 

 in which this double reflection image was very conspicuous ; and 

 there is not the slightest doubt that some lightning-flashes are 

 bright enough to give this secondary image. M. Moussette also 

 showed the photograph of a flash in which the centre of the flash 

 was whitest, with a darker edge on either side. This may have 

 been produced either by double reflection from the lens, or by in- 

 ternal reflection from the back of the glass plate. Two bands of 

 light — the primary and secondary images — slightly overlapping 

 would form an extra bright band where the overlap took place. 



In the majority of cases, the folds of the ribbon formation are 

 most obvious when the course of the flash is square to the width 

 of the folds, and they are but slightly pronounced when in a line 

 with them. This would suggest the idea of a shaking of the cam- 

 •era in the direction of the folds of the ribbon ; but, if this is so, the 

 duration of a lightning-flash must be much longer than is usually 

 supposed. 



The committee hope to have the opportunity of making some ex- 

 periments on the photography of sparks from a coil or electrical in- 

 fluence machine. In the mean time they defer expressing an opin- 

 ion as to whether lightning ever really takes a ribbon-like form till 

 further evidence is available, but would point out that both sources 

 of error — the duplication of the image either by reflection inside 

 the lens, or by reflection from the back of the plate — would be 

 avoided by the use of single lenses, and of paper instead of glass 

 supported films. The committee also forbear for the present from 

 publishing a reproduction of a ribbon-like flash, till they are satisfied 

 that such a form of lightning really exists, and that the whole ap- 

 pearance is not due to photographic causes. 



In one picture, sent by Mr. Shepherd, there are five ordinary 

 white flashes, and one dark streak of precisely the same character 

 as the bright streaks. M. Moussette has suggested that this may 

 be the result of a very bright flash, so over-exposing the plate as 

 to produce the well-known inversion of a negative by over-expos- 

 lure, as when the ball of the sun appears black on the positive 

 iprint, instead of white. This is no doubt a possible explanation ; 

 but the committee would like further examples of this same ap- 

 pearance of dark flashes before expressing'an opinion on the mat- 

 ter. 



The committee call attention to the fact that there, is not the 

 slightest evidence in the photographs of lightning-flashes of that 

 angular zigzag or forked form so commonly seen in pictures. 



In connection with this, they would call attention to a remark- 

 able paper, communicated to the British Association in 1856, by 

 James Nasmyth, F.R.S. Mr. Nasmyth says that he has never 

 seen forked lightning of the angular zigzag form, and asserts that 

 '• the true natural form of a primitive flash of lightning appears to 

 Mr. Nasmyth to be more correctly represented by an intensely 

 crooked line, and on several occasions he has observed it to assume 

 the forked or branched form, but never the zigzag dovetail." 



The Council of the Royal Meteorological Society are desirous of 

 obtaining more photographs of flashes of lightning, as they believe 

 that a great deal of research on this subject can only be pursued 



by means of the camera, and would esteem it a great favor if any 

 one would give them any assistance in this matter, either by send- 

 ing them copies of any photographs of flashes of lightning that may 

 have already been taken, or by endeavoring to procure them, or to 

 interest others in so doing. 



It may perhaps be well to mention that the photography of light- 

 ning does not present any particular difficulties. If a rapid plate, 

 and an ordinary rapid lens with full aperture, be left uncovered for 

 a short time at night during a thunder-storm, flashes of lightning 

 will, after development, be found in some cases to have impressed 

 themselves upon the plate. The only difficulty is the uncertainty 

 whether any particular flash will happen to have been in the field 

 of view. A rapid single lens is much more suitable than a rapid 

 doublet ; and it is believed that films on paper would effectiially 

 prevent reflection from the back. 



The focus should be that for a distant object ; and, if possible, 

 some point of landscape should be included to give the position of 

 the horizon. If the latter is impossible, then the top of the picture 

 should be distinctly marked. Any additional information as to the 

 time, direction in which the camera was pointed, and the state of 

 the weather, would be very desirable. The council hope, now that 

 the thunder-storm season is approaching, many photographers, 

 both amateur and professional, may be found willing to take up 

 this interesting branch of their art. A. F. N. 



New York, July 2. 



The Name of America. 



Will you permit us to correct some erroneous ideas in your 

 note on our work ? Your reviewer, referring to the origin of the 

 name ' America,' says that our account derives it from a Peruvian 

 tribe, although the name was in use long before Peru was discov- 

 ered. This, no doubt, is an unintentional misrepresentation, as no 

 such tribe ever existed, the name ' Peru ' having been given by the 

 Spaniards to the kingdom of the Aymaras of Aymaraca, whose 

 subjects, according to some authors, were also the chief race in 

 the West Indies. Your reviewer also wonders if the author ever 

 knew that the Indies was the recognized Spanish name of the con- 

 tinent during the age of its discovery. 



It seems to us incredible that any one could make such a remark, 

 seeing that every schoolboy knows the story of the naming of the 

 West Indies, while our work refers over and over again to the fact 

 that the continent was officially known in Spain as the Indias, — a 

 general term including the East and West Indies, which contained 

 a large number of countries. 



When a work bases a discovery on the evidence of standard au- 

 thorities, the impartial critic who is not convinced will point out 

 where the evidence is defective. This is the law of logic, which a 

 scholar cannot ignore. But when an author who translates his orig- 

 inal evidence from Italian, Spanish, French, German, and Latin, finds 

 himself designated under the clownish epithets of ' half-learned 

 wanderers,' ' happy enthusiasts,' ' erratic followers,' etc., we will 

 leave it to the public' to say whether that is an impartial, fair, or 

 scholarly critique, or whether it does not look like the work of some 

 little publisher, whose history — always for sale — tells another 

 story. 



The great Baron de Humboldt says that Amaraca-pana was the 

 first Spanish settlement on the mainland. This was in 1502, five 

 years before the pamphlet of St. Die proposed the name of ' Amer- 

 igo Vespucci,' who sailed into Amaraca-pana on his first visit, under 

 command of Ojeda, to the New World, and which was the only 

 place where they were favorably received, and treated as if they 

 were angels. So says the royal Spanish historian Herrara, in 

 quoting Ojeda himself ; and the Isle of Tamaragua, on the first 

 standard map of the continent, published in 1508, was evidently in- 

 tended for Amaraca or America, which was long considered an 

 isle. Here is positive evidence, by well-known authorities ; and 

 whoever is not convinced should point to evidence of a better 

 explanation, or show cause why ours is insufficient ; doing so in the 

 language — to use your reviewer's own words — of a " sober his- 

 torian." T. DE St. Bris. 



New York. June 30. 



[Our correspondent has evidently failed to read the review care- 

 fully.— Ed.] 



