In Rockstro "The flute"  we find that a horse and carriage at the value of hundred and fifty guineas was offered for a flute.
This shows a considerable appreciation for the instrument.
The player of the modern flute might wonder: where does the renewed interest for this far less perfected instrument come from. It is too easy to say: this was the instrument for which the music has been composed and therefore it sounds or plays better on it.
Fact is that many like the eighteenth century music better on original or replicas of original instruments than when played on the modern flute. Clearly this is enough for the revival.
A musical instrument can be considered from different points of view -as object -from the listener -from the player The latter two of course are the more important. However, it is a bit difficult to base a written account on those. Therefore the description necessarily treats the object. It should be stressed though that all three are essential when studying old musical instruments.
It is remarkable that there have been some two centuries only where the bore of the flute has been (inverse) conical. This implies that the cross-section of the bore is larger at the mouth hole than at the foot. This period lasted from the middle of the seventeenth century to the end of the nineteenth century. Before this the flute was a straight tube with six finger holes and a mouth hole. After this period the Boehm flute again is largely a straight tube.
Changes in instruments never happened from one day to the next. Previous forms have been maintained, used and produced long after the introduction of new versions of an instrument. Therefore, I do not want to give the impression that the conical flute suddenly was there or suddenly disappeared. The appearance of the conical flute is nicely illustrated by the Haka flute found in the Utrecht collection. This flute from the famous seventeenth century woodwind maker Haka from Amsterdam, is only slightly conical. The key is there but very small. The conical flute of course is still produced in our century, for instance for Irish music. Even the one keyed flute has been produced until far in the nineteenth century, if not, as has been reported to me in the twentieth century. At the same period as the introduction of the conical flute the first key was introduced. This key together with conical form of the tube give the possibility to tune the flute better. The flute also was subdivided in three pieces instead of two as was usual before.
This is the flute that we now commonly call the Traverso. Quantz, in his standard work  supposes that the conical flute, had been invented in France but confesses not to be sure that he is right. There are indeed a number of flutes from this period originating from France. Those flutes from makers such as Hotteterre, Chevalier etc. are indeed three part conical one keyed flutes. However the above mentioned Haka flute probably is older. In the beginning of the eighteenth century the middle piece of the flute is subdivided in two parts.
After 1720 we find mainly four piece flutes. The four parts are called the head, the left hand part, the right hand part and the foot. There still is only one key.
Tromlitz  states that the reason for the subdivision is the fact that the long middle piece can not be rereamed if necessary when it has warped. In two parts this is far less problematic.
Let us take a closer look at the Baroque traverso. The mouth hole normally is between 8 and 10 mm, round or elliptic. The finger holes are round or almost round. The sizes are 5 to 7.5 mm for the left hand part and 4 to 6.5 for the right hand part. Specially the lowest hole of the right hand part is smaller than the others. The bore in the head is between 16 and 20 mm decreasing towards the foot to between 12 and 14 mm. The bore of the foot often widens again.
The bore is irregular for tuning and tone quality purposes. Local irregularities are a very important means to influence both the tone quality and the tuning.
In the eighteenth century there did not exist a standard diapason. Even organs in neighbouring villages would have a different diapason and tuning. This constituted less of a problem for the string instruments than for the woodwind. The development of the flute from straight renaissance instrument to conical one keyed Baroque flute continues therefore with the development of different means to adapt the diapason. We find warnings in different tutors against just pulling the left hand part out of the head for lowering the tuning as a sufficient means to adapt the diapason. In general the aspects that are decisive for the tuning of the flute are
-the conicity, form and diameter of the bore
-the place and undercutting of the mouth hole and the finger holes.
The place and form of the finger holes of course can not be used for incidental adaptation of the tuning.
Therefore it became fashionable to make traverso with more than one left hand piece. In the beginning the maximum was three with a relatively small spread in diapason. The next development is the screw in the cork to adapt the position of the cork more easily and more precisely to the middle piece chosen. At the same time a "register foot" has been developed. This is a small loose end of the foot that can be used to lengthen the foot also to adapt to the chosen middle piece.
Tromlitz states that with the help of the last two devices five different middle parts are possible with a usable intonation. He does not mention what the range is that can be covered. However there are a number of flutes with five middle parts in collections and musea.
The quality of the different tones on the one keyed flute is not uniform. Some tones are clearly weaker than others. For instance the f1, the g1 sharp and the b1 flat have this property. On bad flutes clearly worse than on good ones. This difference in tone quality is used by composers for colouring the music in a particular way. These effects are probably partly reason for the renewed interest for the replicas of historical instruments.
Also the tuning of the one keyed flute has some problems. The f and f sharp are both tuned with the same hole (five from the top). Therefore they always are somewhat to close with respect to equal temperament. This is compensated with the embouchure. The problem is less than it seems if we consider this from the point of view of pure thirds in various scales.
In the second half of the eighteenth century the requirements for playing in different keys easily are a driving force for changing the instrument. Also the taste with respect to tone quality changes. In the beginning of the eighteenth century the emphasis was on an instrument with a strong first octave. Maybe the makers were not able to provide instruments with a very good third octave. And the music was adapted to that. But most likely the instrument and the music influenced each other. An example of the acceptance of the shortcomings is found in Hotteterre [ 4] where he states that a reliable f in the third octave can not really be expected on the flute. End of the eighteenth century the requirement is also a clear second and third octave and a more penetrating sound. However it should be mentioned that the variety in instruments at the end of the eighteenth century was very large.
To alleviate the deficiencies of certain tones extra keys were added. For instance for the f1 , the g1 sharp and the b1 flat and c1. Different levers are invented to make it easier to handle the keys. A large number of key systems is invented.
In short beginning of the nineteenth century there is real race of key system inventors.
This race simply is won by Mr. Boehm as is well known, giving us the Boehm flute. The flute that is still with us at present as the normal instrument.
 Richard Shepherd Rockstro, The flute. First ed. 1890, Facsimile Frits Knuf, Buren 1986 ISBN 906027507
 J.J. Quantz, On playing the flute, second edition, Faber and Faber, ISDN0-571-18046-9, different facsimile and translation editions. E.g. ISDN3-7618-0074-6 (and a number of other facsimiles,e.g. in Dutch, in German(original) and in French)
 J.G.Tromlitz, Ausfuehrlicher und gruendlicher Unterricht die Floete zu spielen, Facsimile Frits Knuf Buren 1973, 1985
 Jacques Hotteterre, Principe de la flute traversiere etc. First ed. 1707 remark: Knuf no longer exists. They have been taken over by some German company. As soon as I know the details I will give them here.