JULY 22, 1915] 

NATURE 
o70 

may be warmed by the sun while the other two sides 
are cooled by a cold wind. ‘The occupants of rooms 
on these sides may require air ten degrees higher in 
temperature. The individual duct system allows them 
to get it. The direct radiators placed in the class- 
rooms cannot be depended upon to maintain the proper 
balance when a trunk system is used and air of the 
same temperature supplied to every room. The sunny 
side rooms need cooler air, and cannot get it by the 
trunk system. The individual duct system, moreover, 
is excellent in allowing monotony of atmospheric 
conditions to be avoided; a cooler or a warmer air 
may be had at will. 
Mr. Kimball says: ‘* The installation of the indivi- 
dual duct system increases the cost of the ventilating 
plant by two and one half per-cent. in large, and five 
per cent. in small buildings.” It is well worth it. 
He says automatic temperature-controlling systems 
may save ten to twenty per cent. of the annual fuel 
bill, and protect the class-rooms from excessive tem- 
peratures. By thermostatic devices in mild weather 
little or no steam is admitted to the class-room radia- 
tors, and cool air is delivered. In cold weather much 
steam is sent into the radiators and a warmer air 
delivered. Mr. Kimball says a thorough diffusion of 
the air through every portion of a class-room can be 
obtained by one or two fresh-air openings eight feet 
above the floor, with a single exhaust opening on the 
same side at the floor. The inlets should be directed 
towards the windows or be placed in the end walls 
as near as possible to the windows, and the outlet at 
the other end of the same wall near the floor. In 
churches and auditoriums the best results can be ob- 
tained by exhausting through mushroom openings 
near the floor and supplying air through openings 
in the walls or ceiling. The cool incoming air must 
be let in well above the occupants, so as not to cause 
unpleasant draughts. 
In warm weather it is desirable to be able to reverse 
the current and send the cool air in at the floor. 
It is quite easy to arrange for this in the plant. 
Better still, both the in- and out-fans may be altered 
so as to impel into the building air which escapes 
through open doors and windows—an admirable plan. 
The cost of the plant such as sketched above is 
reckoned as about one and a halfpenny per cubic foot 
of space in the building. Only a proper combination 
of fresh-air supply and vitiated-air exhaust will afford 
a good ventilation in an auditorium. No occupant 
should be further than twenty-five feet from a fresh- 
air register or nearer than six feet to a vent register; 
the greater the number of both kinds of registers, the 
greater the satisfaction with the system. Direct 
radiators should be employed to balance loss of heat 
through windows and walls. They should be placed 
under windows, by doors, and along exterior walls. 
A large amount of radiation should be placed in vesti- 
bules to prevent annoying draughts. 
In the temperate climate of Britain we can make 
do with an open fire and window system, which is 
intolerable in places where excessively low winter 
temperatures have to be faced. As, however, central 
heating is coming largely into use in public buildings, 
it is most necessary that it should be recognised that 
the true function of ventilation is to keep up the 
adequate loss of body heat and relieve the cutaneous 
sensations from monotony; that heating and ven- 
tilating systems must be kept separate and planned on 
the lines so well sketched out by Mr. Kimball; that 
architecture must be subservient to the demand for 
proper space, lighting, heating, and ventilation; and 
that intelligent, trained men (or women) are required 
to look after the systems of heating and ventilation, 
and work these so as adequately to cool, and avoid 
the monotony of, the occupants. Ike Isle 
No. 2386, VOL. 95] 

PROBLEMS OF MINE VALUATION. 
HE State of Wisconsin has published a very in- 
teresting Bulletin under the title of “A Study 
of Methods of Mine Valuation and Assessment, with 
special reference to the Zinc Mines of South-western 
Wisconsin,” by W. L. Uglow, which is well worthy of 
the attention of anyone concerned in the knotty 
problems of mine valuation. The Wisconsin Legis- 
lature has decided to impose a tax upon mineral pro- 
perty, which is to be valued on the same principle 
as is applied to all real estate in that State, namely, the 
“full value which could ordinarily be obtained therefor 
at private sale’’; this phrase is not quite clear, but 
apparently means the value that could be realised under 
a sale from a willing seller to a willing purchaser. 
The difficulties that beset such a valuation in all cir- 
cumstances are increased by the fact that in the 
majority of cases these mines are leased by the mining 
companies from the royalty owners, whilst the neces- 
sary capital is often borrowed from banks, so that 
three separate parties are interested in the mining 
property. It is interesting to note that the royalty 
payable to the owner varies from 5 to 15 per cent., 
averaging 10 per cent. on the gross receipts, the 
owner paying as a rule the real property tax upon the 
increased value of his land due to the fact that it is 
mineral-bearing, as well as an income tax upon the 
royalty that he receives. 
Two points of general interest are to be found in the 
treatment of the royalty and of the interest upon the 
capital borrowed for working the mine, the author 
holding that neither of these can equitably be con- 
sidered as an addition to working costs, but that both 
must be looked upon as coming wholly out of profits. 
Probably few will question this treatment of interest, 
but the royalty question appears much more open to 
discussion. Unfortunately most of the other points 
dealt with have only a local rather than a general 
interest, because the ore-bodies are all shallow, and 
the life of mines in this district is consequently only a 
short one, so that the methods of valuation here em~- 
ployed have only a limited application. 
A number of methods of valuation are discussed: in 
detail, namely: (1) The Finlay ad valorem method, 
which calculates the value of a mine as the present value 
of the average annual profits that may be expected to 
be obtained during the life of that mine, setting aside 
an annual sinking fund instalment, the total amount 
of all of which instalments, at the end of the esti- 
mated life of the mine, will amount to the present 
value. (2) The Arizona method, which tales the value 
of a mine for the purposes of taxation as represented 
by one-eighth of the gross production of the previous 
year, four times the net profit of the previous year 
and the value of the improvements. (3) The Colorado 
method, which takes the value as one-fourth of the 
value of the gross output of the preceding year, unless 
the net exceeds one-fourth of the gross, in which case 
the net output is taken to be the assessable value, 
except in the case of mines of the precious metals, 
where the value is taken to be half the value of the 
gross output plus the entire net output. (4) The 
Equated Income method, which takes the value as the 
present value of all future profits, these latter being 
taken as equal to the actual profits of the preceding 
year, excluding royalty, interest, and amortisation 
charges, assuming the same average length of life for 
all the mines of a district. 
The author compares all these methods, and appears - 
to decide in favour of the last-named. He is quite 
alive to the difficulties of the problem, and is also 
careful to point out the fact, too generally overlooked 
in the taxation of mines, that mining property is a 
wasting asset, and on this account ought not to be 
taxed on the same basis as ordinary real estate. 
