Aprit 4, 1884. ] 
LETTERS TO THE EDITOR. 
*,* Correspondents are requested to be as brief as possible. 
The writer’s name is in all cases required as proof of good faith. 
The great comet of September, 1882. 
A MORE recent determination of the orbit of this 
comet than those mentioned in No. 57 of Science 
has been made, and the results may be of interest. 
To avoid (as far as may be) the errors which arise 
from the fact that different observers have observed 
various portions of the nucleus, it was thought best 
to take a series of observations made at a single 
observatory. A fine series of over one hundred 
observations made at Cordoba, and extending from 
Oct. 17, 1882, to June 1, 1883, was chosen. Up to 
Feb. 12, the same portion of the nucleus was observed: 
this portion afterwards became invisible, and then 
the estimated centre of the elongated nebulous mass 
was taken. 
By comparing these observations with an ephemeris 
computed from a former orbit, three normal places 
were found, the four observations made in May and 
June being neglected. The dates of these normal 
places were Nov. 16.0, Jan. 3.0, and March 25.0. It 
is to be regretted that these observations did not begin 
in September, so that the first normal place might 
have been nearer the time of perihelion. Below is 
the derived system of elements, which is referred to 
the mean equinox of 1883.0, Greenwich M.T. 
_ 5. 4) 2) eg Sept. 17.2637 
Cee  . 5. OOS | 2! 61659" 
_ =, MS 345 45 55.01 
Meese. ce Sl e|CUK 4A OB1L54 
Meee se. ee SO) OSC BS 
222 - 0 9.99996 10 
2 ee 7.8821773 
loga. 1.9289 
Period . 782.4 years. 
Perihelion distance 
Semi-major axis 
Semi-minor axis 
_ . .. 707,500 miles. 
- 7,878,000,000 
105,600,000 
These elements satisfy the second normal place 
very closely, the residuals being — 
AA cos B = + 0.02”; AB = +0.02”. 
If the period be assumed as 751 years, on the as- 
sumption that the comet appeared in 370 B.C. and 
1132 A.D., and the foregoing perihelion distance 
be accepted, the logarithm of the eccentricity must be 
9.9999599, which is 0.0000011 less than the value 
given above. 
It is the intention of the writer to combine all 
the reliable observations which have been made, in the 
hope of obtaining a fair orbit for this perplexing 
object. H. A. Howe. 
University of Denver, 
March 11. 
Atmospheric wave from Krakatoa. 
Granting, as stated in Science, iii. 338, that an 
atmospheric wave passing over the entire world was 
caused by the great eruption in the Straits of Sunda, 
would not its greatest effect be observable at the 
opposite extremity of the diameter of the earth, or 
near the northern extremity of South America? The 
wave would doubtless pass away from its origin in 
all conceivable directions, its front forming the arc 
of a small circle, constantly enlarging until it became 
a great circle, after which it would contract, conver- 
ging as to a focus on the opposite side of the earth, 
producing a magnified effect; after which it would 
return as from a second origin. 
Hoboken, March i6. 
SCIENCE, 
401 
Electric time-signals. 
The devices, recently described in Science, by which 
a clock is made to close an electric circuit at regular 
intervals, prompt me to describe a very simple one 
which I have found entirely satisfactory. It is ap- 
plied to a tower-clock as follows: to the arbor carry- 
ing the minute-hand, at the end A, opposite the dial, 
is screwed a slender brass arm about five inches in 
length, extending down to two light metallic springs, 
BC. The brass arm at the proper moment comes 1n 
contact with B, and moves it forward till it touches 
4A 
the platinum point on C. The electric circuit is then 
closed, as B and Care soldered to two brass blocks, 
D E, to which the wires of the circuit are attached. 
These blocks are screwed fast to a piece of wood, F, 
which is in turn secured to the clock-frame by set 
screws. It will be observed that the current does not 
pass through the works of the clock. ‘The appliance 
can be made to close the circuit at any portion of the 
hour by simply loosening the movable hand at A, and 
fastening it so that it shall bring the two springs 
together at the required minute. This arrangement 
has not failed once in a year and a half on a circuit 
including nine bells. H. S. ‘CARHARTT. 
Evanston, Ill., March 17. 
Is material contact possible? 
Dr. John Robison, the eminent Scottish physicist, 
discussing ‘ Newton’s rings’ (about 1795), concluded 
that to produce the central ‘ black spot’ between two 
glasses required a pressure of about a thousand 
pounds to a square inch; the separation at this place 
being still about of an inch. Dr. Thomas 
Young (about 1805) found that the phenomenon does 
not depend on the presence of air. By the general 
consensus of physicists this has been accepted as a 
striking evidence that molecular resistance to absolute 
contact is insuperable. 
Sir William Thomson, in a Friday evening lecture 
at the Royal institution of Great Britain, delivered 
Feb. 2, 1883, said, however, very emphatically, ‘“‘I 
do not believe that foramoment. The seeming repul- 
sion comes from shreds or particles of dust between- 
them” (Proc. Roy. inst., Feb. 2, 1883, x. 189; Nature, 
June 28, 1883). 
As a question of fact, this is one of very great im- 
portance; and it surely deserves a critical and decisive 
determination by some of our well-equipped physi- 
cists. . The investigation, though a very delicate and 
refined one, is quite within the resources of modern 
experimentation. The physical problem is, can the 
‘black spot’ between perfectly clean plates be pro- 
duced without sensible pressure ? W.., By =2. 
