146 Bibliography. 
No. 7. Portable achromatic compound microscope for travelling, 
mounted on three folding-legs, with quick and slow motion, the move- 
able stage is 3 by 4 inches, concave mirror, 24 inches, ~~ 2eye-pieces 
and 4 inch object-glass, packed in a flat mahogany ca 5. ‘ 
. 8. Best single microscope with all iinproveniearg 4 object- 
glasses, varying from 1 inch to $ inch, packed in a small flat mahog: 
any case, to the top of which it is mounted when in use, $40. be 
No. 9. Ditto, simpler, with the same powers, $32-35. oe 
A small compound body with L eye-piece, and 4 inch-object glass, 
is supplied with No. 8 and 9 additional, $15-20 
All accessory instruments and apparatus, as "well as additional ob- 
ject- — and eye- piec es made to order at moderate prices. 
ssrs. Grunow’s instruments are in mechanical structure unsuf- 
eee — 
. American Association for the Advancement of Science.——The 
seed meeting of this Association will be held at Cleveland, Ohio, com- 
mencing with the third Wednesday in August (Aug. 18). Professor 
Peirce of asad; is President for the session and ensuing year 
9. Gold of California.—The total shipment of gold from San Fran- 
cisco for April, 1852, was $3,419,847, for March, $2,549,704. 
VI. Bretiocraruy. 
1. Steam-Boiler Explosions : Memorial of Samuel Guthrie, a Practi- 
cal Engineer, submitting the results of an investigation made by him into 
the causes of the explosion of steam-boilers. 32d Congress, U. 
Ist Session, Senate, No. 32, Miscellaneous. Pi is an excellent doc: 
ument, from an experienced man, who makes no pretensions to being 
more than he is, a skillful practical engineer. Mr, Guthrie has de 
voted many mo onths to a careful investigation of all the causes of dis- 
Pewee CEES 
after eer had exploded. We need not dwell on the preéminent impor 
tance of the adoption without delay of certain and efficient means 
wrediee class of accidents which no warning from past experience not 
check of existing laws have prevented from ge heal 2 with the rapi¢ 
extension of our immense i inland commerce. In ou 
? 
ards and penalties, would reach the difficulty and _ totally pre 
these frightful necidenis so destructi e to human life ‘a carefl 
atin ip of the principal causes tending to produce expl one 
of steam-boilers.— ist. Using iron of an improper ESR DaPSaf or that 
an anietiar quality, i in the construction of boilers ; also, the r quent 
cast-iron in steam and water PIRAPs and parts of ae A 
2a. os boilers defective in for workmanship, ineffectuallf 
lted or fastened ; and also meine en weakened by age or us? 
oyment of i t, reckless, or pipers ep cil 
