312 Notes and Memoranda. 



same principle, but of considerably higher power than that to which he referred 

 with such strong commendation. The subject of our experiment corresponds 

 very closely in power with a Huyghenian eyepiece, estimated at 300, with a 42- 

 inch telescope, having a fine 3-inch Gauss objective, by Steinheil, of Munich, 

 remarkable for the lightness of its field. It is only upon certain objects, and in 

 very fine weather, that such au eyepiece can be fairly tried, but we have obtained a 

 good definition of small stars, and a splendid effect upon the grand mountain 

 scenery near the terminator of the moon before and after its full. The field is 

 rather larger than with the Huyghenian, but the difference is not so great as in 

 lower powers. It is also rather lighter, and on the most, favourable evening of 

 our experiments we were disposed to give it a decided preference for certain objects. 

 From the fact of the surface of the field lens being in the focus of the eye com- 

 bination, extraordinary care in freeing the former from dust is essential. It would 

 not be fair to either the makers or our readers to say more at present, except that, 

 as the new eyepiece is not expensive, we strongly advise astronomers to investigate 

 its merits by actual use. Mr. Webb has employed a miscroscope object-glass 

 for high powers, " the field lens of the ordinary construction being omitted, and 

 the microscope object-glass taking the place of the lens next the eye." This plan 

 works well, but it is too costly for ordinary use. 



Miceoscopic Address Cards. — The minute cards supplied by Mr. Webb 

 are wonderful specimens of microscopic engraving and printing. You receive a 

 Lilliputian glazed card, without the slightest trace of any inscription. A strong 

 pocket lens shows two faint and delicate lines, impossible to decipher : but if the 

 little curiosity is transferred to the stage of the microscope, and examined with an 

 inch or two-thirds objective, you at once see a name and address in elegantly- 

 formed letters, and greatly admire the skill by which so marvellous a result is 

 obtained. 



Fish Hook Spiculje. — We have received from Mr. Baker, of Holborn, a 

 slide containing spiculse of the Hymedesmia Johnsonii (a sponge from Madeira), 

 and which are stated to be new objects in this country. They have the form of a 

 double fish-hook, and on the inner surface of each hook is an extremely sharp knife 

 edge projection, corresponding with a similar and equally sharp projection from 

 the inside of the shank. These minute knife-blades are so arranged that, in addition 

 to their cutting properties, they would act as barbs, obstructing the withdrawal of 

 the hook. The two hooks attached to one shank are not in the same plane, but 

 nearly at right angles with one another, so that when one is horizontal, the other 

 is vertical, or nearly so. A magnification of 400 or 500 linear does not in any way 

 detract from the sharp appearance of the knife edges, and they may take their 

 place with the anchors of the Synapta, as curious illustrations of the occurrence in 

 living organisms, of forms which man was apt to fancy were exclusively the products 

 of his own contrivance and skill. We presume these hooks of the Hymedesmia 

 answer the usual purpose of spiculse in strengthening the soft tissue, but they must 

 likewise render the sponge an awkward article for the Madeira sea slugs to eat. 



\ Determining the Distance of the Sun. — M. Foucault has devised an 

 ingenious apparatus for determining the velocity of light, and from the results thus 

 obtained he computes the distance of the sun from the earth without leaving his 

 study. M. Babinet in stating these facts to the French Academy, observed : 

 " Astronomy by the measure of aberration tells us that the mean velocity of the 

 earth round the sun is lohiru °f ^ na ^ °f light. Taking this fraction of the velocity 

 of light we have the space traversed by the earth in one second, and by multi- 

 plying by the number of seconds in a sidereal year we obtain the dimensions of 

 the annual orbit of the earth. Half the diameter of this orbit is the distance of 

 the suu from the earth. The solar parallax, according to M. Foucault is 8" - 86, 

 with an uncertainty of about ^,. 



