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Four accounts of Berti's experiment exist, but a simple model of his experiment consisted of filling with water a long tube that had both ends plugged, then standing the tube in a basin already full of water. The bottom end of the tube was opened, and water that had been inside of it poured out into the basin. However, only part of the water in the tube flowed out, and the level of the water inside the tube stayed at an exact level, which happened to be 10.3 m (34 ft), the same height Baliani and Galileo had observed that was limited by the siphon. What was most important about this experiment was that the lowering water had left a space above it in the tube which had no intermediate contact with air to fill it up. This seemed to suggest the possibility of a vacuum existing in the space above the water.
Torricelli, a friend and student of Galileo, interpreted the results of the experiments in a novel way. He proposed that the weight of the atmosphere, not an attracting force of the vacuum, held the water in the tube. In a letter to Michelangelo Ricci in 1644 concerning the experiments, he wrote:
Many have said that a vacuum does not exist, others that it does exist in spite of the repugnance of nature and with difficulty; I know of no one who has said that it exists without difficulty and without a resistance from nature. I argued thus: If there can be found a manifest cause from which the resistance can be derived which is felt if we try to make a vacuum, it seems to me foolish to try to attribute to vacuum those operations which follow evidently from some other cause; and so by making some very easy calculations, I found that the cause assigned by me (that is, the weight of the atmosphere) ought by itself alone to offer a greater resistance than it does when we try to produce a vacuum.
It was traditionally thought (especially by the Aristotelians) that the air did not have weight: that is, that the kilometers of air above the surface did not exert any weight on the bodies below it. Even Galileo had accepted the weightlessness of air as a simple truth. Torricelli questioned that assumption, and instead proposed that air had weight and that it was the latter (not the attracting force of the vacuum) which held (or rather, pushed) up the column of water. He thought that the level the water stayed at (c. 10.3 m) was reflective of the force of the air's weight pushing on it (specifically, pushing on the water in the basin and thus limiting how much water can fall from the tube into it). He viewed the barometer as a balance, an instrument for measurement (as opposed to merely being an instrument to create a vacuum), and because he was the first to view it this way, he is traditionally considered the inventor of the barometer (in the sense in which we now use the term).
Because of rumors circulating in Torricelli's gossipy Italian neighbourhood, which included that he was engaged in some form of sorcery or witchcraft, Torricelli realized he had to keep his experiment secret to avoid the risk of being arrested. He needed to use a liquid that was heavier than water, and from his previous association and suggestions by Galileo, he deduced that by using mercury, a shorter tube could be used. With mercury, which is about 14 times denser than water, a tube only 80 cm was now needed, not 10.5 m.
A mercury barometer is an instrument used to measure atmospheric pressure in a certain location and has a vertical glass tube closed at the top sitting in an open mercury-filled basin at the bottom. Mercury in the tube adjusts until the weight of it balances the atmospheric force exerted on the reservoir. High atmospheric pressure places more force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the force placed on the reservoir. Since higher temperature levels around the instrument will reduce the density of the mercury, the scale for reading the height of the mercury is adjusted to compensate for this effect. The tube has to be at least as long as the amount dipping in the mercury + head space + the maximum length of the column.
Sympiesometers have two parts. One is a traditional mercury thermometer that is needed to calculate the expansion or contraction of the fluid in the barometer. The other is the barometer, consisting of a J-shaped tube open at the lower end and closed at the top, with small reservoirs at both ends of the tube.
A wheel barometer uses a \"J\" tube sealed at the top of the longer limb. The shorter limb is open to the atmosphere and floating on top of the mercury there is a small glass float. A fine silken thread is attached to the float which passes up over a wheel and then back down to a counterweight (usually protected in another tube). The wheel turns the point on the front of the barometer. As atmospheric pressure increases mercury moves from the short to the long limb, the float falls and the pointer moves. When pressure falls the mercury moves back, lifting the float and turning the dial the other way.
where ρ is the density of mercury, g is the gravitational acceleration, and h is the height of the mercury column above the free surface area. The physical dimensions (length of tube and cross-sectional area of the tube) of the barometer itself have no effect on the height of the fluid column in the tube.
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Intravenous line was established and pethidine 0.5 mg/kg was administered intravenously. General anaesthesia was induced using intravenous thiopentone sodium 5.0 mg/kg. Vecuronium bromide 0.1 mg/kg was administered to facilitate tracheal intubation. Patient's trachea was intubated by performing direct laryngoscopy in sniffing position using cuffed PVC ET (Romsons Sci and Surg Ltd., Agra, India). Appropriate size ET was selected for tracheal intubation, i.e., 7.0 or 7.5 mm ID for females and 8.0 to 9.0 mm ID for male patients. The tube was placed such that the cuff of the endotracheal tube (ETT) disappeared below the vocal cords and the black mark lay between the vocal cords. The head position was made neutral. The ET was secured by tape at the right angle of mouth. Breathing circuit was then attached and placement of ET confirmed by 5-point auscultation and capnography.
Comparing airway distances measured in our study to those quoted by other researchers and textbooks reveal that the mean airway length from lip to carina is smaller in Indian population. Also, the trachea in Indian patients is considerably shorter. This emphasises the fact that the recommendation to secure the ET at 23 cm in males and 21 cm in females will result in carinal impingement and endobronchial intubation in most of the Indian patients. Moreover, this depth of fixation has been recommended by measuring the airway distances in midline, although the ET is fixed at the right angle of mouth, which is a shorter distance as compared with that in midline. Therefore, securing the tube according to this recommendation will further increase the chances of endobronchial intubation.
As previously stated, various textbooks describe that the depth of placement of endobronchial tube will be adequate when the tip of endobronchial tube rests 4 cm (3-5 cm) proximal to carina.[5,6,14] The basis of keeping these Figures was to allow sufficient distance between the tube tip and carina on one hand, and the tube cuff and cricoid cartilage on the other, to prevent complications associated with movement of head and neck, change in patient position or creation of pneumoperitoneum.
The above mentioned formula can guide optimal depth of placement of oral ET with tube tip 3 cm above carina in Indian adult patients. The mean height in sample population was 166.32 cm in males and 152.14 cm in females. Accordingly, the average depth of fixation of oral ET should be 20.26 cm in males and 18.23 cm in females from right angle of mouth.
Proper placement of ET also requires that the cuff should be well below cricoid. It seems prudent to avoid the cricoid as this part of the airway is a complete ring as opposed to the trachea which has a membranous posterior wall that may act to relieve the pressure of an over-inflated tracheal tube cuff. To know the relation between the position of proximal edge of the cuff and the cricoid, tracheal tubes used in this study, i.e., 7.0, 7.5, 8.0, 8.5 mm ID (Romsons Sci and Surg Ltd., Agra, India), were analysed. We found that the proximal edge of the cuff was 6.0 cm from the ET tip. It was same in all the sizes used (7.0-8.5 mm ID). These are the sizes which are used in most of the Indian adult patients requiring orotracheal intubation. If the tip of ET is placed 4 cm above carina, then the proximal part of the cuff will lie 10 cm above carina. But, the mean tracheal length (SD) in our population was found to be 9.83 (1.26) cm in males and 9.27 (0.99) cm in females. This means that the cuff would be lying inside the cricoid ring in most of the patients. 781b155fdc