The record-union., 1892-03-26
FoGS OVER GREAT CITIES.


Caused By the Presence of Dust in the
Air.
! Among the practical questions with
| Whlch men OF science are called upon
! to deal, few are more interesting than
that OF the origin and nature OF great
! logs. III Is only ABOUT eleven years since
! the true cause Of fogs was discovered.
Mr.. Aitken, an Englishman, demon
! Strated by experiments in lSS0 that fogs
arise from the presence OF dust floating in
! the air. Each minute particle, too small
| III itself to he visible to the eye, serves as
point OF condensation for the moisture
| or the atmosphere, and as the moisture
! gathers the particle becomes speck of
mist. Millions of millions of such parti-
| cles, each loaded with condensed vapor,
constitute fog.
| Careful investigations have shown that
even the clearest air contains an astonish-
lshIng amount of dust, while, as every
! body can see at a glance, the atmosphere
| IN the near cities is filled with micro
! scopIc floating particles that frequently
| rob 1t OF much of its transparency; but
while perfectly clear air seems n thino
earnestly to be desired, yet Mr.. Aitken's
! experiments showed that but for the dust
1 in the air we should probably find exist
ence far more trying than it is now.
| The dust particles being absent, the
| atmospheric moisture would condenSe
| upon the trees, the grass. the ground,
! upon our tlOLDtS diltt ItSCS, upon IIlS
walls, floors and ceilings and houses in
| side and out, so that during such times as
| the air is charged with an unusual amount
/ OF humidity we should be covered and sur
| rounded on ali sides with streams of
| moisture.
| That would probably be the form in
! which we should then Get rain, instead of
| having it fall in showers from the sky as
| it now does.
! Still, although it can thus be shown
/ that dust in the air serves admirable pur-
! poses, IT has, of course, many disagreed
! bic and injurious features. Not the least
| of these is its effect in producing such
| phenomena as the celebrated fog OF Lon
! don.
| Such fogs are not confined to London,
! but occasionally make their appearance
over all large and busy cities, especially
\ those where great deal OF smoke exists.
! The smoke particles not only form ex-
| cellent little conGensers, but they give to
/ the fog that black and gloomy color
/ which is especially noticeable in the fogs
/ OF London. More or less poisonous in
gradients, such as sulphuric acid, are also
/ found in the togs of great cities.
| 1t is natural 10 suppose, and it has often
| been asserted, that such logs largely in
/ crease the death rate of the cities afflicted
| by them: but recent Investigations by w.
j. Russell indicate that while many more
deaths occur in London just after great
/ log, yet it is probable that the real cause
! of the increase is not so much the fog
| itself as the Sudden fail Of temperature by
/ which it is ordinarily accompanied. He
/ finds that fogS not accompanied by TALL
of temperature are not followed by an in
crease in the death rate.
/ By cutting Oft the sunshine, however.
city fogs cause great injury TO health, and
j their destructive effects upon some of the
plants in the great botanic gardens at
Iaas-
fessor Thiselton-Dyer, the director of the
/ Kew Gardens, fears that refined horti-
culture may become impossible in the
vicinity of London If the fogs continue to
increase in number and intensity.
| One remedy recommended is the sub