726 
somewhat pear-shaped, the large end lying ventrally. 
The lumen is retained until the fusion with the me- 
dian part is accomplished by the union of the large 
end of the side components with the central division: 
the large end soon after assumes the characteristic 
net-like form of the thyroid gland; but the lateral 
portions can still be distinguished for some time by 
the lesser size of the meshes, and the greater size of 
the cords of the network into which they change. 
In the introduction to his article, Born refers to 
the previous writings of Stieda and Wolfler, and closes 
with a criticism of the same, and other publications 
based upon his own researches. ‘The most important 
point to be noticed is the correction of Wolfler’s mis- 
take in describing the second cleft as the first. (In 
this abstract, the author’s arrangement of the matter 
has not been followed, as it appeared little conducive 
to clearness). C. S. MINorT. 
RESEARCHES ON ASTRONOMICAL SPEC- 
TRUM-PHOTOGRAPHY. 
At the time of his death, in November, 1882, Dr. 
Henry Draper had, for a number of years, been large- 
ly occupied with very tedious and costly investiga- 
tions connected with the photography of the spectra 
of the heavenly bodies, his unusual adaptedness for 
the prosecution of which research conducted him to 
results of the highest importance. With true scien- 
tific spirit, Mrs. Draper has generously placed at the 
disposal of Professor Young and Professor Pickering 
all the data necessary for the proper publication of 
the work; and, in a monograph of about forty pages, 
the former gives an introduction to Dr. Draper’s 
researches, together with a description of the appara- 
tus with which they were made, extracts from the 
original note-books, and a list of the photographic 
plates in Mrs. Draper’s possession; while the latter, 
who took a number of these plates to the observatory 
of Harvard college in the spring of 1883, presents the 
results of his measurements, accompanied by a dis- 
cussion of the plates. 
Dr. Draper’s attention appears to have been first 
turned toward spectrum-photography in 1869 and 
1870, although his photographic work in other fields 
previously to this time had been singularly successful. 
His first work in science, conducted while a medi- 
cal student in New York, and which related to the 
function of the spleen, was illustrated with micro- 
photographs of great excellence; and very soon after 
taking his degree, while on a visit at Parsonstown, 
Ireland, he became so thoroughly impressed with the 
photographic possibilities of the great reflecting-tele- 
scope of the Earl of Rosse, that, soon after his return 
home, he began the construction of a metallic spec- 
ulum of fifteen inches diameter, which was soon re- 
placed by a number of silver-on-glass mirrors of about 
the same size, the details of the construction and 
mounting of which formed the subject of one of the 
Smithsonian contributions to knowledge, published 
in 1864. Seven years later, he had completed with 
his own hands the entire construction and mounting 
of a twenty-eight inch silvered-glass mirror, with 
SCIENCE. 
[Vou. III., No. 71. 
which he obtained, in May, 1872, his first photographs 
of the spectrum of a Lyrae by merely inserting a 
quartz prism in the path of the rays, just inside the 
focus of the small mirror, and employing neither slit 
nor lenses. Three months afterward, the same 
method secured for him plates showing four lines in 
the spectrum of the same star. For two or three 
years following, Dr. Draper’s time was, for the most 
part, occupied with other lines of work, connected 
with investigations of the solar spectrum, and the 
superintendence of the photographic preparations for 
the transit of Venus of 1874. He returned to the 
subject of stellar spectra in 1876, obtaining a num- 
ber of photographs with a fine twelve-inch refractor 
by Alvan Clark & Sons. This instrument, now the 
lesser telescope of the Lick observatory, was re- 
placed in Dr. Draper’s establishment, in 1880, by an 
eleven-inch Clark refractor, which was provided with 
a correcting-lens fitted to be placed in front of the 
object-glass to adapt it to photographie work. This 
instrument was mounted on the same set of axes 
with the twenty-eight inch Cassegrain mirror, as were 
also a finder of five inches aperture, and one of two 
inches, — all of which are well shown in the picture 
of the telescopes in the Hastings observatory, vol. i. 
of Science, p. dl. 
Dr. Draper’s eminent successes in celestial photog- 
raphy were due in large degree to his own skill and 
discoveries in the manipulation of the sensitized 
plates. Until 1879, wet collodion plates were used 
in all his experiments; but after that time he em- 
ployed exclusively the dry plates made by Wratten & 
Wainwright, to the admirable performance of which, 
in the hands of Dr. Huggins, his attention was ealled 
by that distinguished astronomical physicist, on a 
visit of Dr. Draper to England in 1879. 
Professor Young directs attention to the fact that 
the investigations of stellar spectra were by no means 
carried on continuously, but only during Dr. Draper’s 
summer residence at his country-place, and in the in- 
tervals of other, to him, even more absorbingly in- 
teresting researches and urgent business occupations. 
The difficulties proved to be well-nigh insurmount- 
able; for at first the limitations imposed upon the 
time of exposure by the use of the wet process made 
it almost impossible to get impressions of sufficient 
strength, — a difficulty which vanished on the intro- 
duction of the modern dry-plate processes: and an- 
other difficulty, increasing with the length of the 
exposure, was that of securing a sufficiently accurate 
movement of the driving-clock. No less than seven 
such clocks were constructed before he succeeded in 
getting a perfect one. Its regulator was a pair of 
heavy conical pendulums, so hung that their revolu- 
tions were sensibly isochronous through quite a range 
of inclination. The gearing and driving-screw were 
constructed, for the most part, by Dr. Draper himself, 
with the utmost care and accuracy; and Professor | 
Young says, that, in its ultimate perfected condition, 
the driving-clock was as good as any in existence, be- 
ing able to keep a star upon the slit for an hourat a 
time, when near the meridian, and not disturbed by 
changes of refraction. 
