144 Short Papers and Notes. 
coleoptera, spiders, and aphides more favoured in this respect. 
Again, some ichneumons are in their turn attacked by other 
ichneumons, which are then said to be “ hyper-parasitical ;” a 
case of this kind is recorded in Zhe Lntomologist for May, it 
having been observed that the larvae of Pimpla scanica are hyper- 
parasitical on those of Lamneria vulgaris. 
The common cabbage butterfly (P. vafz@) and magpie moth 
(Abraxas grossulariata) are very liable to attack from ichneumons, 
which are thus of very material use in keeping the ravages of these 
destructive insects in check. It always happens that a super- 
abundance of any insect is met by a corresponding increase in the 
numbers of the ichneumons which attack it. So that the more these 
interesting insects are studied, the more we must admire them, not 
only for their individual points of interest, but also for the very 
important part they play inthe economy of Nature, in affording a 
constant check on the too-rapid multiplication of any one species 
of insect. 
Short Papers and Notes. 
Curious Jrormation of Crystals. 
F a lump of granulated pure chloride of ammonium be carefully 
introduced into a solution of nitrate of lead, best in a wide- 
mouthed bottle, there will soon appear pillars of crystals 
resembling, in some respects, the amorpho-crystalline snow- 
banks. The result is very beautiful ; but, besides, affords an 
excellent opportunity to notice the mode of formation. The 
minute crystals of chloride of lead will be seen to rise from all 
sides, at the base of the forming pillars, and, ascending above 
their summits, will describe an inward curve and fall ontop. This 
process being continued, the pillars will rise rapidly. This is 
interesting as bearing on the causes of crystalline form. If the 
commercial fibrous chlorides of ammonium be used instead of that 
described, the result is extremely remarkable from an artistic point 
of view, but does not show the currents so distinctly. 
Al Modern Barometer. 
A very good and sensitive barometer may be made by glueing 
together strips of red cedar and seasoned pine. __A strip of cedar, 
about thirty inches long, one-and-a-half inches wide, and one- 
eighth of an inch in thickness, is cut with the grain, and to one 
side of it must be glued strips of pine of equal thickness, with 
, 
