228 Royal Society. 
stars ; gave a history of the alterations which he has noticed in’ 
the aspect of the sidereal heavens, during the last 30 years ; 
and described those stars which have increased in magnitude, or 
brilliancy, have lost or acquired surrounding nebula, or have 
had wings, tails, or other peculiarities. He seems inclined to 
believe, from his observations, that new sidereal bodies are in 
a constant and progressive state of formation, that nebulous ap- 
pearances gradually assume a globular character ; that the hea- 
vens are not infinite, and that stars have a ‘‘compréssing power.” 
He considers the origin.and progress of sidereal bodies to be 
nearly in the following order : first, vague and indistinct nebule, 
like the milky way ; second, detached or clustered nebule, which 
consolidate into clusters of stars; thirdly, these stars becoming 
more definite appear with nebulous appendages in the different 
forms of wings, tails, &c.; and lastly, that all are finally concen- 
trated into one clear, bright, and large stare Dr. H. concludes 
that the progressive discovery of nebulz will be equal to the im- 
provement of our telescopes, and that in proportion as we are 
possessed of more powerful space-penetrating instruments, will 
our knowledge of the sidereal heavens be extended. Many of 
his latter observations directed to ascertain the absorption or con- 
densation of nebulz were made on stars, which he had before 
described in his numerous papers in the Phil. Transact. ; others 
were made on those whose places have been determined by foreign 
astronomers. 
March 10. Mr. Seppins, one of the surveyors of the Navy, in 
a letter to the President, described his new system of ship-build-. 
ing; he observed that notwithstanding the rapid progress in all 
the arts and sciences, no improvement in nayal architecture has 
taken place during many years. In order to make the simple 
but great improvement which he has introduced more intel- 
ligible, he began by describing the old structure of ships, of 
their keel and ribs or timbers placed at right angles, and the 
bottom and decks composed of parallel planks. According to 
the new construction, on which three ships have already been 
built, and four more are building, the timbers are crossed with 
diagonal girders at angles of 45, so that the whole frame is ren- 
dered much stiffer or more inflexible, and all parts of the struc- 
ture made to bear their due portion of the pressure at the same 
time. The first advantage of this plan is the prevention of 
what is called hogging, or having the centre become convex on 
the upper, and concave on the lower side. Mr, Seppins fills up 
the space between the timbers with pieces of wood taken from 
old ships, made in the form of wedges, which are reversed, driven 
in tight, paid with tar, and made impervious to water, so that 
should an outer plank start, the vessel will be in no danger of 
sinking 
