42 
POPULAE SCIENCE NEWS. 
[Makcti, 1S90. 
temperature, it is a perfectly safe and health- 
ful means of warming buildings. The dis- 
advantages of a furnace are due to other 
causes than from its "burning" the air. It 
is also a mistaken idea that steam heat is 
moister than any other kind. Air heated by 
passing over a radiator is in exactly the same 
condition as when heated by a furnace, and 
tlie only possible way in which it could be 
moistened would be by the escape of steam 
from a leakv valve, which, however, is by no 
means an uncommon occurrence in many of 
the radiators in use. 
PRE-HISTORIC ROCK INSCRIPTIONS 
IN SWEDEN. 
No part of Europe has given richer returns 
to the student of archasology than the countries 
of Norway, Sweden, Denmark, and, perhaps, 
Finland, generally grouped together under 
the name of Scandinavia. From the verj' 
earliest times they seem to have been occu- 
pied by a large and 
energetic popula- 
tion, and the nu- 
- merous deposits of 
weapons, imple- 
ments, and utensils, 
— whether of stone, 
bronze, or iron, — 
show a perfection 
and beauty ex- 
ceeded or scarcely 
equalled b\' those 
of no other pre-his- 
toric races. 
The advanced 
state of the early 
civilization indi- 
cated in tlie Scan- 
dinavian coimtries, 
tends to confirm 
the doubtful theory 
that the great Aryan immigration startctl 
from this region ; or that more prepos- 
terous assertion, tliat the north polar 
regions were the true cradle of the human 
race, and were, in former times, blessed 
with a temperate climate and a luxurious 
vegetation. No scientist of any reputa- 
tion, however, supports this wild idea, and 
the best authorities consider that the use of 
bronze and other metals was introduced into 
the Scandinavian countries from other parts 
of Europe, and did not originate with the 
ancient inhabitants, no matter to what per- 
fection they afterwards brought the foreign 
arts. 
M. Victor Rydberg has recently been 
studying the curious rock inscriptions which 
are quite abundant in Sweden. We repro- 
duce two engravings of these cuttin»s, one 
(Fig. 1) showing a ledge near Bohuslan cov- 
ered with representations of boats filled with 
men,, and the other (Fig. 2) showing the 
details of a similar rock sculpture in the 
parish of Brastad. The age of these sculp- 
tures is still in doubt, but the best authorities, 
including the Marquis of Nadaillac, — from 
whose description in La Nature we repro- 
duce the accompanying engravings,— agree 
in referring them to the age of Bronze,"which 
came to a close not later than 1500 B. C. 
This age is particularly indicated by the 
wheel-shaped solar emblems, shown in Fig. 
3, and the absence of the svast/'ka, or sacred 
symbol of the Aryans, which was not intro- 
duced into Sweden until after the commence- 
ment of the age of Ir(5n. 
The objects represented in the Swedish 
rock sculptures are very numerous. The 
ancient boats, with high bow and ornamented 
stern, are very common, and were probably 
the models after which the later ships of the 
Vikings were constructed. Many animals 
are represented, including oxen, foxes, dogs, 
various birds, and reindeer attached to a 
sledge. Hmnan figures, are common, and 
of Sweden, the peasants deposit in these 
cupules ofierings for the souls of their 
departed children, whiclr are supposed to be 
wandering in space, waiting for an oppor- 
tunity to enter once more into a human body. 
Fig. 1. 
generally represented as naked, but some- 
times clothed in a long robe descending to 
the feet. Certain of these figures are appar- 
ently represented with tails, but this is 
undoubtedlv an unskillful attempt of the 
ancient sculptor to represent the extremity of 
the arm. 
At Tanum a certain number of men are 
represented as walking in Indian file, and 
deprived of their arms. These are supposed 
to represent captives in war, submitted to a 
cruel mutilation ; or, more probably, it is 
only another indication of the sculptor's lack 
of skill. Other inscriptions closely resemble 
those of the North American Indians, and 
suggest the question of a possible ancient 
emigration to this country. Many religious j 
symbols have been noted, such as wheels, 
crosses, and cupules, or cup-shaped depres- 
sions, doubtless connected with ancient 
religious rites. To this day, in certain parts 
Fig. 2. 
The future study of these inscriptions, 
which M. Rydberg has so successfully beg-un, 
will undoubtedly greatl}^ increase our know- 
ledge of those interesting pre-historic times 
of which so many relics have come down 
to us, but of 
which we realh- 
know so little. 
All our historical 
records are but of 
yesterday, and we 
cannot doubt that, 
back of the races 
of which \\e have 
a direct know- 
ledge, the earth 
has been inhabited 
for many thousands 
of years by suc- 
cessive generations 
of men, who have 
left scarcely any 
more traces of 
tlieir existence 
than the leaves of 
the trees in their annual growth and decay. 
[Original in l*opular .S'ciCHc'C Xews.} 
BRIEF STUDIES IN BIOLOGY. 
BY PROF. JAMES U. STOLLER. 
11. 
■fllE HYDRA. 
As a bubject for our second study, we inay take 
the, little animal found everywhere in ponds attached 
to the (' nes of water plants, called the hydra 
{Hydra viridis or Hydra fiisca.) This animal, 
which is a sort of classic in zoology, — having been 
famous since 1744, when Tremblej, the Swiss natu- 
ralist, did his curious experiments upon it, — is a 
representative of the second great division of the 
animal kingdom, viz. : the Coelenterata. 
The general form and aspect of the hydra, as seen 
under a low power of the microscope, is shown in the 
accompanying figure (page 43.) It is seen that the 
body consists of a trunk-like part, attached at its base, 
and of six or eight radiating arms, or tentacles, at 
the free end. (The bud-hydra connected with the 
trunk will be referred to below.) The mouth is 
situated at the free end, and opens into the body- 
cavity, which is simply the hollow of the trunk. 
The body-cavity is also the stomach, and it is from 
