SCIENCE. 
263 
volving mirror, and the fixed mirror at a distance of about 
2000 feet. By this arrangement, with a speed of rotation 
of 257 turns per second, he obtained a deflection of 1 1 5 
millimeters; whereas, Foucault using a speed of 400 
turns per second, and causing the light to traverse a 
distance of 20 meters, had obtained a deflection of 8 
millimeters. The revolving mirror was driven by a tur- 
bine-wheel operated by a blast of air. Its speed, which 
was measured by an electric tuning-fork, was readily 
adjusted by a stop-cock, and the deflection was measured 
by a micrometer. 
Mr. Michelson gives a most careful discussion of the 
errors of his constants, including the determination of the 
value of the micrometer screw, the rate of vibration of 
the tuning fork, etc., and concludes with the considera- 
tion of several ‘‘objections ” which have been suggested 
from time to time. 
The final value for the velocity of light in vacuo is 
299944 ±51 (in air, 299864), or, in round numbers, 
299940 kilometers per second = 186380 miles per second,* 
the remarkably small error, + 51 kilometers, being com- 
posed of the total constant error in the most unfavorable 
case, and the probable errors of observation. This quan- 
tity, + 51 kilometers, cannot be said to express \hz prob- 
able error of the determination, in the ordinary accept- 
ance of the term ; combining, as it does, probaole errors, 
strictly speaking, and estimated constant errors. 
These experiments were made by Master Michelson at 
the Naval Academy, Annapolis, at private expense, and 
to him the entire credit is due. A new determination of 
the velocity of light, embodying essentially the same ar- 
rangement, but with more elaborate and expensive appa- 
ratus, is now being made under official auspices by Prof. 
Newcomb, Superintendent of the Nautical Almanac. 
It is probable that in this way the most accurate value 
of the solar parallax, so essential to astronomy, can be 
deduced. 
Astronomical Memoranda. —^Computed for the 
meridian of Washington, D. C., November 29, 1880) : 
H. M. S. 
Sidereal time 05 mean noon 16 35 50 
Equation of time 1 1 15 
mean noon following apparent noon. 
The Sun is 21° 39' south of the equator, at meridian 
transit, and will continue to move south until Decem- 
ber 21. 
The Moon reached its last quarter on November 24d. 
8h. 47m. It does not come to the meridian until 10 A.M. 
of November 30. 
Mercury was in inferior conjunction, November 23, 
and is not now visible to the naked eye. It precedes the 
sun by about 52 minutes, and is five degrees farther 
North. 
Venus is plainly seen in the southwest ; a short time 
after sunset ; following the sun by 2h. 33m., and gradually 
increasing the distance. Its declination is 24 0 43' south. 
Mars is at present too close to the sun for observa- 
tion. 
fupiter, though gradually growing fainter, is still the 
most brilliant object in our eastern sky at evening. It 
passes the meridian at 8 P.M., at an altitude of 54 0 above 
the southern horizon. Its more exact position at that time 
is : Right Ascension, oh. 37m. 43s.; declination, +2 0 28'. 
Saturn, less brilliant than Jupiter, is, notwithstanding, 
equal or superior to the larger planet in point of interest. 
It isreaddy found about 13° E. by N. of Jupiter, present- 
ing a good view of the southern side of its rings. 
Uranus is in right ascension iih. om. 52s. declina- 
tion + 7° 9'. 
* Note. — Foucault’s experiments gave the velocity as 185200 miles per 
second. 
Neptune is in excellent position for observation, reach- 
ing the meridian at about io P. M. It was in opposition 
on November 4, and may now be found in Right Ascen- 
sion 2h. 41m. 27s. declination +13 0 46'. 
A new 10 in. equatorial, with an object glass by 
Merz, has been presented to the Geneva Observatory by 
its director, Prol. Emil Plantamour. It is to be devoted 
to observations of the major planets and their satel- 
lites, ot parallax of stars, and ot double stars, with oc- 
casional observations of minor planets. 
Dr. Schmidt has made a new determination of the 
time of rotation of Jupiter upon its axis, from observa- 
tions in 1879 and 1880, of the red spot upon its disc. 
His preliminary discussion gives for the time of rotation 
9h. 55m. 34.42s. 
In a letter to Nature, dated October 2, Prof. Picker- 
ing, ot Harvard College Observatory, announces that the 
period of Ceraski’s new variable star is probably 2.5 
days, instead of 5 days, as previously published by 
Scnmidt. It is especially remarkable for the rapidity cf 
change during part of its period. The total variation is 
from about the 6.7th to the 10th magnitude. The ap- 
proximate place for 1881 is, R. A. oh. 51m. 48s. Dec. 
+ 81 0 14'. 1. W. C. W. 
Washington, D. C., Nov. 23, 1880. 
MICROSCOPICAL COLLECTIONS IN FLORIDA* 
By Dr. C. C. Merriman. 
It has been my fortune during the past two Winters to 
spend a few weeks in the regions of Central Florida. Lake 
Harris is the most southern and the most beautiful of the 
cluster of lakes which forms the source of that exceedingly 
picturesque river, the Ocklawaha. With high banks, and 
surrounded by a belt of hummock land as rich as any that 
Florida affords, this lake is becoming settled upon, and its 
lands are fast being taken up by enterprising southerners 
for orange-groves and pine-apple plantations. The so- 
journer will find the society of this lake-settlement intelli- 
gent and hospitable beyond anything that would be ex- 
pected in so new and pioneer a country. The vegetation 
of this almost tropical region is so full of interest to the 
microscopist, and the causes conducing thereto so peculiar, 
that I have thought them deserving of especial mention and 
illustration. 
The absence, or at least the rarity of frosts injurious to 
vegetation in these lake districts, gives the longest possible 
season for the growth and maturity of such organs as are 
best, or especially, adapted to the exigences of Florida 
plants. There is a period of rest, usually comprising about 
the three Winter months, after which vegetation takes up 
and continues its growth again as if there had been no 
period of interruption ; so that practically there is a conlin- 
ous development of plant life, whether annual or perennial, 
from birth to death. 
The soil of Florida, as of all the South-Atlantic sea- 
board, is sandy and naturally barren. No polar glaciers 
have ground up for these regions, as for the Northern 
States, a rich and abundant alluvium, sufficient in itself for 
the production of a rapid and vigorous vegetation. The 
South has apparently only the siltings of our Northern soil, 
carried down to the ocean by rivers, and then washed up by 
the sea-waves to form their interminable sandy plains. But 
to compensate for this natural infertility of soil, the atmos- 
phere, especially of Southern Florida, abounds in all the 
elements of plant growth. The winds which come up from 
the Gulf on one side, or the Atlantic on the other, are 
charged with moisture, and bear also minute quantities of 
nitric acid and saline compounds ; while the exhalations 
from the swamps and marshes furnish in abundance the 
salts of ammonia and carbonic acid. Now to utilize these 
precious products from the air, it is necessary for plants to 
*Read before the Sub-section of Microscopy of the A. A. A. S. 
