80 Notes and Memoranda. 



Prisms and Silvered Fiats for Telescopes. — A paper by Mr. Browning 

 will be found in Monthly Notices, comparing the action of a prism and a silvered 

 flat when used with the glass reflecting telescopes. The prism he finds to reflect 

 more light, as might have been expected, and he found that when a prism and a 

 flat, placed side by side, threw down two pencils of the light from a. paraffin 

 lamp, that the circle of light from the prism looked white, while the other was 

 strongly tinctured with a reddish chocolate colour. We have made experiments with 

 prisms and flats fully according with Mr. Browning's results. The prisms, if 

 accurate in form, are far superior to the silvered flats in light and colour, and 

 quite equal to them in point of definition. Mr. Browning exhibited to the 

 Astronomical Society a fine prism made for Mr. De la Rue. 



Fungus in A Tree. — The Archives des Sciences has an account of a paper 

 by Signor Gasparini, in which he states that a fine Acacia dealbata from New 

 Holland, when in full flower in a garden at Naples, was broken through its stem 

 by a slight blast of wind. It was found that the heart wood was black and rotten, 

 and microscopic examination revealed the mycelium threads of a fungus. The 

 medullary rays, pith, and spiral vessels were not attacked, but the dotted vessels 

 (vaisseaux ponctues) were so. Signor Grasparini considered that the spores of the 

 fungus had introduced themselves through the rootlets. He states that when the 

 spangioles have been broken in plants of the lily tribe, spores have found entrance, 

 and occasioned damage. 



Strange Effect oe Lightning. — Cosmos states, on the authority of M. 

 Saillant, that on May 15 an oak was struck by lightning in the forest of Yibraye 

 (Sarthe) at about two-thirds of its height, at the origin of the large branches. 

 The upper third, comprehending the crown and its branches, was not touched, but 

 the remainder of the tree was split to shivers, and dispersed in all directions. No 

 vestige was found of the bark, the root was partly torn up, and a heavy fragment 

 hurled more than fifty paces. " The most curious thing is that the top of the 

 tree was stuck in the ground, just where the original trunk was, so that the 

 trunk and roots must have been swept away the time the tree-top took in 

 falling." 



Achromatic Eve-pieces for Telescopes. — For ordinary use the Huyghenian 

 eyepiece will probably remain the favourite for achromatic telescopes, though for 

 extent of field Home and Thornthwaite's aplanatics are preferable. For reflecting 

 telescopes, now coming into more general use since the success attained by Mr. With 

 and Mr. Browning in making and mounting the silvered glass mirrors, the Huy- 

 ghenian eye-piece scarcely works as well as it does with the achromatic. In the 

 latter case the Huyghenian eye-piece corrects errors which do not exist in reflectors. 

 Mr. Browning has constructed a series of achromatic eye-pieces to work with the 

 silvered glass reflectors, and, after giving them many trials, they appear to us 

 decidedly advantageous where smallness of field is not objectionable. If a good 

 Huyghenian eye-piece is employed on Saturn or Jupiter, and then an achromatic 

 of the same power, a noticeable improvement in definition is obtained. Thus the 

 divisions in Saturn's ring can be seen with the achromatic eye-piece when the 

 Huyghenian will scarcely indicate them. We recommend those who possess 

 reflectors to try Mr. Browning's achromatic eye-pieces. 





