Notes, 
456 
tained in contaCt by the pressure of a small piece of paper folded 
in form of a V. The vibrations of the diaphragm of the re- 
ceiving apparatus cannot be written, since the movements of the 
style, however delicate the apparatus, can scarcely be distin- 
guished upon the lamp-black. To enlarge the magnetic vibra- 
tions of the receiver, the cover and the diaphragm of a Bell’s 
telephone are taken away, and on the wood of the instrument 
there is fixed the end of a small, stiff, steel spring. The other 
end of the spring abuts on the surface of the magnetic nucleus, 
surrounded by its coil ; to this extremity is soldered a small mass 
of soft iron weighing about 10 grms., and upon this mass, and 
in the produced line of the axis of the spring, is fixed a light 
style of bamboo, 10 centimetres in length, and terminating in a 
slender whalebone pen. 
An improved siren with an eleCtro-magnetic regulator is 
described by M. Bourbouze in the “ Comptes Rendus.” By 
means of this instrument sound can be made to pass from 
8162 vibrations per second, through all the intermediary notes, 
to 128 vibrations. 
The following resolution respecting the standard unit of 
Micrometry bas been passed by the Royal Microscopical So- 
ciety : — “ That, in the opinion of this Society, the i-iooth of a 
millimetre is too large a unit for micrometric measurements, 
and that it is not expedient at present to prescribe by any formal 
resolution the adoption of a fixed standard for Micrometry.” 
The oil immersion objective has been made successfully by 
Messrs. Powell and Lealand. 
Herr Zeiss proposes the following fluids as substitutes for oil 
of cedar wood for use with oil immersion objectives : — 
1. Chloride of cadmium in glycerin (CdCl 2 ), 1*504. 
2. Copaiva balsam oil, 1*504. 
3. Chloride of zinc in water (ZnCl 2 ), 1*504. 
4. Sulpho-carbolate of zinc in glycerin, 1*501. 
Prof. Abbe considers the chloride of cadmium in glycerin very 
good optically, but somewhat too thick for convenient use. The 
oil of copaiva balsam is in every respeCt equal to oil of cedar 
wood, but not quite so fluid, and therefore better adapted to 
objectives of such large working distance as the ^th. Chloride 
of zinc is not suited to prolonged observations, as after a few 
minutes’ use it deposits small crystals on the slide and front 
lens : great care is required in the use of this and other aqueous 
fluids, lest the brass setting of the objective should be corroded. 
Platinum has been suggested as a material for mounting the 
front lens, but Herr Zeiss has found that its want of rigidity is 
fatal to its employment, as it will not stand when turned to the 
mere shell required. 
