suses.

Except for the comparatively unimportant auxiliary engines reported by municipal stations, in which there was a small decrease in horsepower per machine, there was in every instance a pronounced increase per station and per machine for the total, for all machines, and for each class of machine reported at both cenThe smallest increase in total average capacity is shown for steam engines which, when compared with the large average power of the steam turbines, indicates that when great units of steam power have been required the steam turbine has been utilized. It is apparent, however, that since the figures for steam turbines were combined with those for steam engines in 1902 a correct understanding of the relative averages can be obtained only by the addition of the two sets of figures for 1907. The averages thus secured, for the totals of this combination, show that the increase in steam power has been on a par with that of the other kinds of primary power.

As might be expected, every class of machine reported by the commercial stations not only averaged much larger than those of the municipal stations but the increase in capacity also was greater.

The averages contained in Table 31 are based upon the horsepower as shown in Table 21, while the number of stations reporting the various kinds of power is shown in the following statement:

A total of the number of stations in this statement would be in excess of the actual number reported, since a station having several kinds of power would be repeated under each class of power with which it was equipped.

Dynamos, central stations, and electric railways.— The electric-generating machines in the central stations and electric-railway plants represent the majority of those in use in the United States, and in order to show statistics for the aggregate the totals for the two branches of the industry are combined in Table 32.

With the exception of the dynamos in the isolated electric plants and telephone and telegraph offices, which are comparatively unimportant, the equipment. covered by this table may be accepted as representing all dynamos used for the generation of electricity for general commercial and municipal use.

The total dynamo capacity as reported for the combined industry increased 2,322,044 kilowatts, or 110 per cent, of which increase the central stations contributed 1,496,990 kilowatts, or 64.5 per cent, and the electric-railway plants 825,054 kilowatts, or 35.5 per cent. It is suggestive of the intimate relation existing between the electric generators and the pri

2 Not reported.

mary power, the force necessary to operate the dynamos, that the percentage of increase of the primary power, 106.5 per cent, should so closely approximate that of the dynamos, which was 110 per cent. The evenness of these gains is somewhat remarkable, because both for primary power and for the generators the totals represent the equipment, all of which is not necessary for present requirements. That is, the primary power no doubt represents a larger horsepower than was actually required for electrical purposes at the time of the census, as in many instances plants were equipped to furnish power in connection with other industries conducted by the companies report

ing, as well as with a view to future demands, emergency uses, etc. Similarly the total installation of dynamos represents not only the dynamos required to generate the current actually used, but includes those held in reserve to furnish additional current when needed and to provide for breakdowns or repairs.

Of the total number of dynamos reported, the proportion in central stations was practically the same at the two censuses, i. e., 79.6 per cent in 1907 and 79.1 per cent in 1902. The proportion of kilowatt capacity of the dynamos in the central stations increased, however, from 57.4 per cent in 1902 to 61.1 per cent in 1907.

The direct-current, constant-voltage dynamos showed a total increase in capacity of 292,551 kilowatts, or 27.7 per cent, the greater part of which increase, 216,156 kilowatts, or 73.9 per cent, was for electric railways, while but 76,395, or 26.1 per cent, was contributed by the central stations. Of the total kilowatt capacity of these machines, the electricrailway plants reported nearly seven-tenths in 1907 and a proportion but slightly smaller in 1902.

The direct-current, constant-amperage machine was not reported by the electric-railway plants, as it is not adapted to that service, and the uses of the machine. are so restricted that comparatively few companies doing a general light and power business feel justified in carrying a class of dynamo only fitted for series arc lighting. The number of this class of dynamos reported by the central stations in 1907 was less than one-half the number so reported in 1902, and the decrease in their total capacity amounted to 64,874 kilowatts, or 44.5 per cent.

The alternating single-phase and polyphase current dynamo showed the largest actual and percentage of gain, due to the fact that it is adapted to almost every use required of a dynamo. The total capacity of these machines increased 2,094,367 kilowatts, or 230.3 per cent. Of this gain, 1,485,469 kilowatts, or 70.9 per cent, was represented by the central stations. Electric-railway plants reported a little more than one-fourth of the total capacity of these dynamos in 1907 and not quite one-fifth in 1902.

Table 33 shows the per cent distribution, by kind, of the dynamos in the central stations and electricrailway plants for 1902 and 1907.

Notwithstanding the increase of 27.7 per cent in the total capacity of the direct-current, constantvoltage dynamos in 1907, they represented only about three-tenths of the total capacity of all classes of dynamos in that year as compared with one-half of the total in 1902. The capacity of the alternatingcurrent dynamos, which in 1902 represented but

little more than four-tenths of the total for all classes, had increased its proportion to more than two-thirds in 1907. The direct-current, constant-amperage dynamos, as already stated, were all reported by the central stations, and the small proportion which they supplied of the total kilowatt capacity decreased from nearly 7 per cent in 1902 to slightly less than 2 per cent in 1907.

TABLE 33.-Central electric stations and electric railways-Per cent distribution, by kind and by number and capacity of dynamos: 1907 and 1902.

Dynamos in central stations.-As compared with the total kilowatt capacity of all dynamos reported in 1902 there was an increase in 1907 of 1,496,990 kilowatts, or 123.5 per cent. Of this increase, the commercial stations reported 1,401,354 kilowatts, or 93.6 per cent, and the municipal stations only 95,636 kilowatts, or 6.4 per cent. In 1907 the commercial stations reported 92.3 per cent of the total dynamo capacity and the municipal stations 7.7 per cent. When compared with similar proportions for the prior census it is found that the percentage for the commercial stations was 1.7 per cent greater than in 1902.

The increase in the number and in the capacity of the dynamos of the different kinds in commercial and municipal stations is shown by the figures in Table 34, while Table 35 gives the per cent distribution of such dynamos, by kind, for 1907 and 1902.

The advantages possessed by the alternating-current dynamo and its adaptability for general centralstation work is illustrated by the tremendous gain in

Practically the entire increase in dynamo capacity was due to the gain made by the alternatingcurrent machine, as the direct-current, constant-amperage machines lost 64,874 in kilowatt capacity, which was but little more than counterbalanced by a gain of 76,395 kilowatts in the capacity of the direct-current, constant-voltage machines.

The increase in the total average capacity of the dynamos per station and per machine, shown in Table 36, is in keeping with the general tendency toward larger units of equipment in almost all branches of central-station work.

For the direct-current dynamos there was an increase, although not very pronounced, both per station and per machine. The constant-amperage dynamos in the municipal stations form the single exception to an increase, the average capacity of these dynamos showing a decrease per machine from 48 to 44 kilo

watts. There has been a large decrease in the number of this latter class of dynamos and probably but few new ones installed, and the figures indicate that those removed have been the machines of the larger capacity. In harmony with the great increase in the kilowatt capacity shown for the alternating-current dynamo in other tables, the table of average capacity shows an increase in every detail presented.

A better understanding of the dynamo equipment of central stations may be obtained from a study of the detailed statistics showing the number and capacity of the different types of machines, grouped according to size. The totals for the United States are summarized in Table 37.

TABLE 37.-Central electric stations-Kind of dynamos, by class, number, and kilowatt capacity: 1907.

tion of the six classes ranging from only 14.1 per cent for the class of the lowest total capacity to 19.4 for the class of the highest. Beginning with the class with the smallest kilowatt capacity, the proportions of the total capacity for all kinds of dynamos contributed by the alternating-current were as follows: 61.5; 72.4; 83.1; 88.9; 98.4; and 100 per cent, the proportion thus steadily increasing with the capacity of the dynamo.

In Table 38 the dynamos in commercial and municipal stations, respectively, have been grouped according to the capacity of the separate machines.

and polyphase

current.

200 but under 500 kilowatt capacity: Number...

1.547

Total:

Kilowatt capacity.

434, 586

500 but under 1,000 kilowatt capacity:

9,491

664, 440

24.5

3,128 183,865 45.2

1,664 71,649 88.5

4,699 408, 926

18. 4

2,000 but under 5,000 kilowatt capacity: Number...

163

1.547

434,586

16.0

417 115, 155 28.3

16 4,833 6.0

1,114 314,598

5,000 kilowatt capacity and over:

14.2

Number...

Kilowatt capacity.

Of the direct-current, constant-voltage dynamo capacity, 73.5 per cent was represented by the machines of less than 500 kilowatts; 24.7 per cent by those in the two classes 500 but under 2,000 kilowatt capacity; only 1.7 per cent by those in the class "2,000 but under 5,000 kilowatt capacity;" and none in the class "5,000 kilowatt capacity and over."

The direct-current, constant-amperage machines show even a larger proportion in the small classes, the class of "under 200 kilowatt capacity" having 88.5 per cent, with small proportions in the next three classes and no dynamo of this type of 2,000 kilowatt capacity or over. The remarkable increase in the use of the alternating-current dynamo has already been shown, and its adaptability to the varying requirements as to capacity are demonstrated by the evenness of its distribution among the several classes, the variation in the propor

25142-10- -4

This table shows in every class not only the great preponderance of the dynamo capacity of commercial over municipal stations, but also the little use of dynamos of large capacity in the municipal stations.

The increase in dynamo capacity is practically confined to the states for which statistics are given in Table 39.

The total increase in the dynamo capacity of these 21 states, each of which made a gain of over 20,000 kilowatts, amounted to 1,256,929 kilowatts, or 84 per

cent of the total increase for the entire United States. To illustrate the extent to which single-phase and polyphase dynamos have superseded the other varieties of machines, the increase in their kilowatt capacity is shown separately and is found to approximate closely the total increase for all machines, the difference for the selected states being but 2,361 kilowatts, or less than two-tenths of 1 per cent, and that for the entire United States 11,521 kilowatts, or about eight-tenths of 1 per cent. In some states the increase in the capacity of the alternating-current machines exceeds that for all classes of dynamos; due to the fact that there was an actual decrease in the capacity of the direct-current machines in several states.