Dimensions London Paris Berlin Petersburg Height Breadth 1771 1794 1832 1825 1835 1828 1825 in inches in inches L s d L s d L s d L s d L s d L s d L s d 16 16 0103 0101 0176 087 076 081 0410 30 20 146 232 2610 11610 1710 0106 1210 50 30 24 2 4 11 5 0 6 12 10 9 0 5 5 0 3 8 13 0 5 15 0 60 40 67 14 10 27 0 0 13 9 6 22 7 5 10 4 3 21 18 0 12 9 0 76 40 43 6 0 19 2 9 36 4 5 14 17 5 35 2 11 17 5 0 90 50 84 8 0 34 12 9 71 3 8 28 13 4 33 18 7 100 75 275 0 0 74 5 10 210 13 3 70 9 7 120 75 97 15 9 354 3 2 98 3 10

The price of silvering these plates is twenty per cent on the cost price for English glass; ten per cent on the cost price for Paris plates; and twelve and a half on those of Berlin.

The following table shews the dimensions and price, when silvered, of the largest plates of glass ever made by the British Plate Glass Company, which are now at their warehouse in London: 

Height Breadth Price when silvered
 Inches Inches L s. d.

132 84 200 8 0 146 81 220 7 0 149 84 239 1 6 131 83 239 10 7 160 80 246 15 4

The prices of the largest glass in the Paris lists when silvered, and reduced to English measure, were: 

Year Inches Inches Price when silvered
                        L s. d. 1825 128 80 629 12 0 1835 128 80 136 19 0

207.  If we wish to compare the value of any article at different periods of time, it is clear that neither any one substance, nor even the combination of all manufactured goods, can furnish us with an invariable unit by which to form our scale of estimation.  Mr Malthus has proposed for this purpose to consider a day’s labour of an agricultural labourer, as the unit to which all value should be referred.  Thus, if we wish to compare the value of twenty yards of broad cloth in Saxony at the present time, with that of the same kind and quantity of cloth fabricated in England two centuries ago, we must find the number of days’ labour the cloth would have purchased in England at the time mentioned, and compare it with the number of days’ labour which the same quantity of cloth will now purchase in Saxony.  Agricultural labour appears to have been selected, because it exists in all countries, and employs a large number of persons, and also because it requires a very small degree of previous instruction.  It seems, in fact, to be merely the exertion of a man’s physical force; and its value above that of a machine of equal power arises from its portability, and from the facility of directing its efforts to arbitrary and continually fluctuating purposes.  It may perhaps be worthy of enquiry, whether a more constant average might not be deduced from combining with this species of labour those trades which require but a moderate exertion of skill and which likewise exist in all civilized countries, such as those of the blacksmith and carpenter, etc.(1*) In all such comparisons there is, however, another element, which, though not essentially necessary, will yet add much to our means of judging.