286 
PROCEEDINGS OF THE SOCIETY. 
a tripod. It would be seen that this w r as achieved by making the back 
leg double, and as this was pivoted to the body and capable of consider- 
able lateral movement, it readily adapted itself to any surface on which 
it might be placed, and secured at the same time all the advantages of a 
non-tilting four-footed instrument, with the stability of the tripod. The 
instrument was fitted also with a sliding bar, a horse-shoe opening to 
the stage, a very well arranged substage which would take an Abbe 
condenser, and a coarse- and fine-adjustment with differential screw, and 
it could be supplied at so low a price as to come within the means of 
any English student. He was very glad to see such an instrument in 
the English market. 
The President thought this was very likely to prove a very useful 
instrument ; it was certainly superior in point of steadiness to anything 
of the kind yet produced. His only doubt about it was whether, in 
spite of the strong spring fitted to the joint of the back leg, it might not 
at some time or other work loose. 
Messrs. Watson and Sons exhibited a new superstage-plate which 
was fitted with two steel springs which pressed against the upper plate. 
It was intended to be fitted to the top stage-plate of an ordinary Micro- 
scope. They also showed a Ramsden’s screw micrometer made of 
aluminium, resulting in a reduction in weight from 11 oz. to 5 oz. ; and 
an Abbe camera lucida, also in aluminium, in which the weight had 
been diminished in similar proportions. 
The President said this was not the first time that Mr. Watson had 
taken advantage of the superior lightness of aluminium, and it would be 
readily understood how great the advantage was in the present instances, 
of relieving the eye-piece from the weight of the apparatus placed upon it. 
Mr. R. T. Lewis said he had brought for exhibition two slides recently 
sent to him by Mr. Arnold W. Cooper, of Natal (elected a Fellow of 
the Society at their meeting in January last) which he thought would 
be of some interest. The objects were the larval and perfect forms of 
a kind of scale insect which appeared to be doing some mischief to 
lemon-trees in the colony. He had been able to identify it as being one 
of the Psyllidse , a family of Homopterous Insects occupying a place be- 
tween the Coccididae and the Aphides, and it appeared to be identical with 
Trioza pellucida , a species originally found and described by Mr. Maskell 
in the Transactions of the New Zealand Institute in 1878. Its appear- 
ance in Natal was worth noting, as possibly another instance of importa- 
tion. Mr. Cooper was intending to establish a vivarium, in which it 
was hoped he might be able to trace out the life-history of many similar 
creatures with equal success. 
Dr. Dallinger said that the following letter had been received from 
Dr. H. G. Piffard, of New York, but as he did not state if the condenser 
he used was chromatic or achromatic, it was very difficult to come to any 
conclusion as to the results which he seemed to have arrived at. 
“ I have recently ascertained that several of Powell and Lealand’s 
water-immersion lenses belonging to their series of N.A. 1*26 will 
