MR. IVATT’S NEWEST GREAT NORTHERN ENGINES.

By CHARLES Rous-MARTEN.

It has fallen to my lot to describe in these columns several important improvements effected or new departures taken by .Mr. H. A. Ivatt since he assumed the locomotive superintendency of the Great Northern Railway on the lamented death of his eminent predecessor, Mr. Patrick Stirling, in 1K96. I have set forth successively how, beginning with the re-building of the late Mr. Stirling’s famous single-wheelers, in such sort that while retaining all their well-known characteristics, they should by means of enlarged boiler power and fire-box space he rendered better able to grapple with the more arduous duties now imposed upon them. Mr. Ivatt next proceeded to develop the 6ft. bin. coupled class, which had long done excellent service on heavy stopping trains and light expresses, but usually had failed to keep time with trains that were both fast and heavy; and, finally, how he produced an entirely novel design, so far as British practice went, his ten-wheeled four-coupled engine, No. 990; and I have given specimens of the work accomplished by each class under my own personal observation. I come now to some further developments effected by Mr. Ivatt since the date of my last article.

First, let me observe that the improvements made in Mr. Stirling's 6ft. 6in. coupled design consisted in the provision of a larger boiler, higher steam pressure (170 lb.), and a dome. These have been supplied to all the Stirling coupled engines that have come in for re-building, as also to several of the Kft. and 7ft. 6in. single w heelers of Mr. Stirling's build. But the first new coupled engine actually built by Mr. Ivatt (No. 400) was accorded the great advantage of a leading bogie as well, in place of the single pair of leading wheels under the middle of the smoke-box, with which an undue length of rigid wheel base bad been caused.

As it happened, the next ten coupled engines built by Mr. Ivatt were without bogies, and it was at first feared that he was reverting to the old rigid wheel-base design. The explanation is, however, that the frames for ten of the old design had already been made, and so the engines were finished as six- wheelers, but with increased boiler power.

Since then Mr. Ivatt has constructed no fewer than fifty additional engines of this class, but all with leading bogies, like the pioneer of thp type. No. 400. They are numbered 1071- 1080, 1801-1820, 1841-1860. The improvements have made them very useful "all-round" engines, and they can do what I never found the older Great Northern coupled engines able to do; that is to say,  they can keep time with heavy fast trains, while doing equally well the duty for which their predecessors were designed. It is only fair to the late Mr. Stirling to say that he did not design his coupled engines for first-class express work, and always disliked to see them employed in such duty, which he held could be far more efficiently performed by his fine single-wheelers.

So satisfactory was the working of these coupled engines of the "400" class that Mr. Ivatt determined to bring out a modification of the type designed expressly for running fast and heavy passenger trains. It should be dearly understood that the earlier "400" type were intended simply as an improvement upon the Stirling engines, which were built for mixed traffic duty, without materially diverging from that pattern.

But the bigger boiler and higher steam pressure, supplemented by a dome and a bogie, had rendered them so much more efficient when they had to be employed in express service that it seemed probable they would be equal to all the ordinary express requirements of the line if provided with still greater boiler power.

 Accordingly, while retaining the 6ft. 6in. coupled wheels and the 17in. by 26in. cylinders, Mr. Ivatt adopted a boiler with 6in. additional diameter. 1250 square feet of heating surface instead of 1128 square feet. 120 square feet of fire-box heating surface instead of 108ft and 20.8 square feet of fire-grate area in place of 17.8ft. These expanded dimensions involved the lengthening of the coupling-rods by 3in., the shortening of the chimney, and the bulging out of the boiler over the driving-wheel splashers.

Of these engines, twenty-five have been built. They are numbered 1321-1840 and 1861-1865. They have a very massive and powerful appearance, and in my experience have always done excellent work. Of this I shall have something to say later. But there was yet another fresh type to come.

Mr. Ivatt has always avowed himself a most cordial admirer of the splendid single-wheelers designed anti built by his predecessor. Their sole drawback - as in the case of the coupled engines built by the same eminent engineer- was limited boiler power.  But whereas .Mr. Stirling's coupled engine had only 916 square feet of heating surface, his 7ft. 6in. singles and his 8ft. singles, excepting the last six, had 1045 square feet.

That, however, was excessively small for engines required to perform such arduous duty, and it has always been a puzzle to myself, as well as to other professional observers, how these remarkable locomotives could possibly do the work which I have seen with boiler power so small.

But in the case of the last six 8ft. single-wheelers built by Mr. Stirling, Nos. 1008-1008. this incongruity was even exaggerated, for they had only 1031 square feet of heating surface, notwithstanding that their cylinders were, in the case of five of them 19½ .in. in diameter, or 1½ in.  larger than those of the earlier type, while No. 1008 had 19in. cylinders. There appeared no satisfactory way of getting materially larger boilers on to engines with driving wheels 8ft. 1½ in. in diameter, within the limits of the British loading gauge. On the other hand, the 7ft. 6in. singles. -7ft. 7 7½ in. with new tires — had not only wheels 6in. lower but also piston-stroke 2in. shorter, say 26in. instead of 28in., and as they appeared able to do everything that the 8ft. engine could, and to do it just as well,

Mr. Ivatt resolved to try an experiment with this class by treating it exactly as he had already treated the coupled type, in retaining the Stirling dimension of higher steam pressure, a dome and a bogie. The result was the construction at the Doncaster Works of "No. 266" to replace one of the old engines designed by Mr. Archibald Sturrock, with 7ft. coupled wheels, but rebuilt by Mr. Stirling as single.

The new No. 266 has 7ft. 6in. single driving wheels - 7ft. 7 1/2in. with new tires; cylinders. l8in. by 26in.; a large boiler with centre 8ft. 6in. above the rail level; 1269 square feet of heating surface; fire-box, 7ft. in length; steam pressure, 170 lb. to the square inch, and a four-wheeled bogie under the leading end of the engine, instead of a single pair of leading wheels.

Mr. Ivatt generously insists that the chief merit of the design is Mr. Stirling's, and that he has merely modified that gentleman's design, while he disclaims any pretension to novelty in the new engine; but I must take leave to differ from him on this head. It seems to me that the modifications introduced by Mr. Ivatt are so important and valuable as to constitute "No. 266" an absolutely fresh type of Great Northern engine, and I hold the same opinion with regard to the 1321 coupled class.  Each is a new departure on the Great Northern Railway, and one of great value. I am glad to learn that the "266" type is being multiplied, ten having been put in hand at the Doncaster Works.