234: PROCEEDINGS OF SOCIETIES. 
Mr. Archer showed in the same gathering, but not nearly so 
numerous, conjugated examples of Peniwm closterioides. The 
zygospore of this fine species has hitherto been unknown. It is, 
however, what might be @ priori predicated for it, a broadly elliptic, 
thick-walled, smooth zygospore, and placed between the shortly 
deciduous empty parent cells. 
Mr. Stoney submitted to the Club reasons which appeared 
to him, in the present state of science, to require the general 
adoption by scientific men of the subdivisions of the metre in 
estimating micrometrical magnitudes. He observed, too, that 
all confusion and inconvenience arising from the use of fractions 
may be avoided by a very simple extension of the nomenclature 
of the metrical system, which he thought himself justified in 
recommending to the Club, from the assistance he had himself 
received from it. 
The following table contains what little is needed to enable 
microscopists to determine the values of their present scales in 
parts ofa metre. 
The Metre is defined by the Act which has legalised the use of 
metrical weights and measures in the British dominions, as equal 
to 3937079 inches, which is almost exactly 16 millimetres short 
of 40 inches. Hence 
The Decimetre—the Hand-breadth or Palm—which is th of a 
metre = 1°6 millimetres less than 4 inches. 
The Centimetre, which is ;4,;th or ,420f a metre = 1°6 Vth- 
metres less than ;4,ths of an inch. 
The Millimetre, which is z,55th or 753 of a metre = sth ofan 
inch, with sufficient exactness tor ordinary microscopical purposes. 
(An inch = 25-4 millimetres almost exactly.) 
| | A centimetre divided into millimetres. 
tH 
| 
Four tenths of an inch. 
The Fourth-metre, which is =5}5,th or 75 0f a metre = 34,th 
of an inch. 
The Fifth-metre, which is +5¢5p th or zhs of a metre = 54,5th 
of an inch. 
The Sixth-metre, which is z55h55 th or yo. of a metre = 
sshooth of an inch. 
The Seventh-metre, which comes next, is a measure almost too 
small for microscopical purposes, since the wave-lengths of light 
range between 4 and 8 VIIth metres. 
Every microscopist should habituate himself to estimate the 
sizes of objects when viewed under the several powers with which 
he is accustomed to work. For this purpose, it is well to deter- 
mine the diameter of each field of view, and also to fix on the 
memory the appearance with each lens of objects of the standard 
