j'i4 



NATURE 



\ytdy 3T, 1879 



group of Cincbonaceje," which is distinguished by numpvons 

 seeds in each carpid, though both are included in the same family 

 of Rubiacea;. 



10. (P. 407). — The conical mound of the Flamingo is not at 

 all an error in natural history. I have seen several of these nests 

 with the eggs on the top of the heap on the Roques Islands, 

 north of La Guaira. 



11. (P. 412). — Vulpes cancnzvi-tis. There is no species of 

 true Vulpss in South America, if we follow the distinction 

 established by Burmeister (" Syst. Uebersicht der Thiere Brasil.," 

 i. 92), and the animal in question is undoubtedly the Cams can- 

 crivorus, Desm. 



12. (P. 431). — " Kuramanni Wax. This is composed of the 

 wax of a wild bee (Ceroxyhn andicola), mixed with a pitch-lilvc 

 substance obtained from several trees, chiefly the Maam-tree." 

 It is scarcely possible to believe that the accomplished editor of 

 the "Wanderings" should have penned these lines, where a 

 noble palm of the Andes is changed into a wild bee. The latter 

 is most likely a species of Melipoma. The Kurunianni wax 

 may be identical with a pitch-like substance, called Caraman, 

 Paraman, or Peraman in Venezuelan Guayana, and which is 

 obtained from Moronoiaa. coccinea, Aubl. 



13. (P. 434). — The mahogany tree belongs to the family of 

 Meliacese, but not to the group of Cedraceao (or better Cedrelerc). 



14. (Ibid.). — Maribunta is not a Portuguese word signifying a 

 wasp. In Brazil the word maribondo is used for a certain species 

 of wasp, but the name is taken from tlie Tupi language. 



15. (P. 440). — Mosquito. Even in popular works on natural 

 histoi-y authors should call everything by its real name, and it is 

 therefore altogether wrong to speak of the bites of mosquitoes ; 

 stitig would have been just as short, and evidently more correct. 



16. (P. 447). — Pataca. Perhaps we may read /arora, one of 

 the names of Orialida motinot, Wagl. 



17. (P. 4>3). — Sting Pay. Tiygon pastinaca is a maritime 

 species ; but there are several other ones in South American 

 rivers, as Tr. hystrix, &c. 



18. (P. 473). — Sugarcane is Saccharum (not Saccharinum) 

 officinarum. 



19. (P. 474). — "The tiger-birds derive their popular name 

 from the peculiar cry w-hich they utter." What pow-erful lungs 

 they must have, these tiger-birds, in order to be able to roar like 

 a jaguar ! This singular blunder might have been avoided by 

 reading carefully what Waterton says (p. 195), that it has no 

 song, its name being due to the black spots on a yellow ground 

 on breast and belly. 



20. (P. 475). — The tortoise of Guayana, as far as I know, is 

 Testudo tahulata, c^WeAMorrocoi in Venezuela. Cistudo Carolina 

 is a North American species. 



21. (P. 236). — Chigoe. What Waterton says of the hatching 

 of this animal within the body of man is certainly not true. The 

 eggs are develojied outside, the larvo: leading a free existence. 



Some of the foregoing remarks refer to mere clerical errors (a 

 good many less important ones having been passed over in 

 silence) ; but there are unfortunately not a few inaccurate, and 

 even wholly erroneous statements which we were sorry to find in 

 this Explanatory Index. A. Ernst 



Caracas, May 15 



Swift's Comet.— Williams College Observatory 



I HAVE computed a set of elements of the comet lately dis- 

 covered by Mr. (now Dr.) Swift. They are from observations 

 made by Prof. Lewis Boss, Director of the Dudley Observatory 

 at Albany, on June 24, June 30, Jidy 8. They are these : — 



y April 27-i8oi, M.T. Washington. 

 log. q 9'95<^9"S 



« 45 41 10-5, i- ' 



I 107° I' S3"-6) '"/y"- . 



For the middle observation c-o A \ + o"'6 



A + O" 3 



Or in space, both co-ordinates, about o"'5. 

 They were computed by Olbers' method, afterwards varying Af 

 by the regular rule. A trifling change of Af, which I have not 

 now time to make, would bring a closer representation of the 

 middle observation ; say to about -^o"■2 and -o""i in longitude 

 and latitude respectively. 



I am happy to say that the observatory of this college is to be 

 repaired and put into active operation. It is about forty years 

 ' Diit. of perihelion from n:de. 



old — the oldest I believe in the United Slate; — and was built by 

 the late Prof. Albert Hopkins. It now contains a 74 inch equa- 

 torial, an early work of Clark ; a 3i-inch Simuis tra.sit, of the 

 style of forty years ago, with a very poor object -ghss; and a 

 sidereal clock by Molyneux and Cope, still in good order. I 

 have been authorised by the Hon. David Dudley Field to procure 

 a meridian circle witli telescope of about 5 inches aperture. 



The gentleman just named is the founder of my professorship, 

 the "Field Memorial Professorship of Astronomy," and it is 

 probable that in future a portion of the duties of that professor- 

 ship will consist in making observations, and in their complete 

 discussion. Truman Henry Safford 



Williams College, Williamstown, Mass., U.S.A., July 11 



Electric Lighting 



In the evidence given before the Committee on Electric Light- 

 ing, some mention was made of the difficulty of equalising the 

 light over any considerable area ; but it is worth while to remark 

 that by a simple form of reflector it is possible to make the light 

 very approximately uniform over an area whose radius is twice 

 the height of the lamp above the ground. For imagine a sphere 

 with the lamp as a centre and its height above the ground for 

 radius. Supposing the lamp radiates equally in all directions, 

 the surface of this sphere will be uniformly illuminated, and its 

 surface has an area ^ir/i^. If now we take a plane circular area 

 about the foot of the lamp-post with radius R such that — 



tR^ = 47rh^ or R = 2h, 

 it is plain that by a proper distribution by reflection of the light 

 which would pass through the imaginary sphere outside the solid 

 angle subtended at the lamp by the plane circular area, the illu- 

 mination over that area may be made uniform and equal in 

 intensity to that near the foot of the lamp-post. 



To fi nd the proper form for the reflector, which is of course a 

 surface of revolution, it is necessary to find the angle which 



each zone of the reflector subtends at the lamp in terms of the 

 angle in which the light is reflected by it. This is given by the 

 equation — 



sm<i,d,i> = (^^-y^- lye, 



with the condition <l> = o, when 6 = tan" 2, where taking the 

 lamp-post as the polar axis, the upper end being north, (90 - <p) 

 is N. latitude of that zone of the reflector which sends out its 

 light in S. latitude (go - 9). The polar differential equation of 

 the curve for the reflector may then be easily found ; it is — 



d<b ^9 + <b 



p -i = cot — -~r. 

 dp 2 



A figure of the curve is given below at R R' . The surface of the 

 reflector is swept out by the revolution of R r' round A a'. The 

 dotted portion rK' should be replaced by a separate zone shown 

 at f, but the chief value of this will be as a screen to prevent the 

 light from being visible at low altitudes, the small quantity of 

 light reflected by it merely going to reinforce the illumination in 

 the immediate neighbourhood of the lamp. Such reflectors 

 might be applied with great advantage to powerful lights placed 

 at considerable elevations. A. Mallock 



Brampford Speke, near Exeter, July 14 



