The sun., 1878-08-09
MANUFACTURING MIRAGES.
DY WHICH OBJECTS THOUSANDS OF
MILES DISTANT MAY BE SEEN.
Mr.. james Greshnm's Method of Ascerta aiming
She Exact Whereabouts of ships at Sea
Satisfactory Result OF his Experiments.

Mr. james Gresham. Method Of A.certaining
she Exact Whereabouts Of ships at Sea
satisfsctory Result OF his Experiments.
TO photograph ship on the high seas,
distant from 100 to 5000 miles. giving the name
the latitude and longitude. and the destination
taken from chalk marks on her deck. is prob
lem the solution OF which Mr.. James Gresham
OF 233 Greenwich street is working out
At the first glance the notion would seem TO
have emanated from disorganlzed brain. or to
have been the imagining OF a dreamer Such
however lis not the case. The idea is the result
OF long series Of experiments by q practical
mochanician. one OF whose inventions. the sub
marine travelling torpedo. charged with explo-
sive asphaltum. has gone far toward revolution
izing naval warfare.
Tho phenomenon OF the mirage is well
known to most seamen. Under peculiar atmos-
pheric conditions. ships and prominent points
are often made visible by them on the apparent
horizon at distances varying from so TO $50
miles. These figures are invariably seen in
verted. or. as photographers say. negatively.
The theory OF Mr.. Gresham is founded upon
the mirage. In fact. he has discovered method
of producing an artificial mirage. the principle
Of which he says is the same as that which re-
fleets in the middle Of the desert OF Sahara tho
images of likes and waters thousand miles
distant
A year ago last spring Mr.. Gresham received
an order for coating OF asphatum for the roof
Of one OF Joseph Stiner's tea stores. at Hudson
and Spring streets. He says: My men were
engaged in mixing asphaltum and coal tar in n
caldron. over hot fire in the street. in front Of
the store. 1t was n clear. sunshiny after
noon and was walking about the roof. max
ing the usual examination. Suddenly a dense
black smoke arose from the street below. and
knew the men had upset the cauldron. and that
its contents had ignited ! knew there was no
danger Of firing the house. and | was curiously
watching the great masses Of black smoke roll
Ing overhead. Suddenly sunbeam shot
through them. and beheld sight shall never
forget. Pictured In the same weird form that
have seen distant ships take nt sea during q
mirage, observed distinctly large brig lying
| M n wharf at Hunters Point on fire. The whole
| scene was sharp and distinct One body OF
men. with the hose. were throwing water on the
| burning vessel, and another gang were casting
| of the lines from the schooners that were made
| fast to an adjoining wharf / could even dis
Linguish the different sails as they caught fire.
| | saw tongue Of lame run up the fore shrOuds
| and at the cross trees ignite the tOgalant sails.
! and thence run up to the royal. | could scarce
| ~ believe my senses. by this time the ilre en-
| gines were playing upon the cauldron Of
! nsphAl,um Ia the street and my men came up
/ 10 tell me- the cause Of the accident. Their
| names are Thomas Casey and George Combes.
They are employed 10y me yet | pointed out
the phenomenon, to them; and they; too. were
overwhelmed with astonishment They recog-
| ni2rd the locality rs Hunters Point. and saw
! q" other objects as clearly as dld myself.
| Whom tho fra from tho asphaltum was eX-
! tinguiShed. and the smoke blew away. the
| mirage disappeared
| filed with petroleum. and this latter substance
| and asphaltum are the only ones that have
been able 20 find that will produce the artificial
| mirage. | saw that had made an important
! discovery. and at once set about making a ma
| chine by which / could reproduce the mirage
3n tin; THIS | have succeeded in DOING but
monstrated TO my complete satisfaction that.
| with the proper appliances on board the mas
| ters Of two vessels. 900 or even 1000 miles
apart. may. with the art tincal mirage. not only
see each others vessel but read each other =
name. latitude and longitude from chalk marks
on their respc tive decks. All that would be
sis of a f.w pounds Of asphnltnm, with a cen
! ser To- burn II in. and small battery 10 heat the
wires 10y which ii should BE- surrounded. After
the marine insurance companies ascertain the
that al vessels -hal carly ,the necessity afpa-
! rntus. Thus they will be cOgnizant OF the
whereabouts. Of tho vessels upon which they
! have sold risks"
what Mr.. Gresham proposes TO do. At 4 o'clock
precisely. on a clear afternoon. clouds Of car
boniierQms smoke shall be- sont up from ships
at sea. The names ot the vessels, their latitude
and longitude, and the port where bound, arc
marked in, chalk in large letters on their
Respective decks; Then the Photographic in
The following might be taken as a result; On
one vessel the bieture taken is that Of a full
| riggcd ship. The marks on the deck are:
" Ship Achilles. Latitude o south. longitude
80 west from New York, bound 10 san Fran
| cisco" On the other vessel the picture taken
! presents the following: Bark Brothers. I.ati-
tude 5O' north, longitude 65' west, from Liver
one ship is therefore on Cape ST. Roche. tho
| most easterly point Of South America. AMI the
bark within twcnty-iour hours Of New York.
| The two vessels are more than 1000 miles
apart. When the bark arrives in New York the
consienees Of the ship Achilles ascertain that
| thnlr vessel is safe and on the proper course.
Mr.. Gresham is about thirty-three years OF
| age. and when speaking on the subject OF his
inventions he Is very earnest and animated.
| His words come fast, and his language is always
An understanding Of the theory Of the natu.
| raj mirage Will lead TO more thorough oppre-
citation Of Mr dreshams manner Of producing
| the artificial mirage.
A mirage is an appearance Of distant objects
IN the air, rs If standing in Tho sky or reelected
| from the surface ot waters. IL is produced by
| refrartion in strata OF different densities de-
crcasing or increasing rapidly; and sometimes
| hy rcfraction and reflection combined. Mhcr,
the phenomenon is manifested over the surface
OF water. and where the lower strata of air nr,
cooled hy the water SO Ms to bo donscr than the
upper the course Of tho rays is shown in the
drawing in the suhioined diagram. A Vesse
which may be- so distant as 10 be partly or en-,
tlrely hidden 10y the curvature Of the earth will
appear inverted above the horizon. When the
rays of light are nt first reiracted from the per
pendicular until the critical angle Is reached al
the stratum. then total reelection takes place
10y which the ray Is given nm inclination down
ward. so that the object appears in the direction
seen in an erect position, Will take place whcf
the RAYS II light from II reach the eye before
total reelection takes place. or before tho crlu
leal angle Is reachvl,