Kotlin Design Pattern, Problem with Observer

I tried different ways, but the outcome is still not the way it should be. I have to create a small weather app in Kotlin with some Design Patterns.

interface Sensor {
fun getTemperature() : Float

}

class RandomSensor () : Sensor {
override fun getTemperature(): Float {
    var randomTemp : Double = Random.nextDouble (0.0, 40.00)
    return randomTemp.toFloat()
}

}

class Thermometer (var sensor: Sensor)  {

var newTemp = this.sensor.getTemperature()

val tempwerte = mutableListOf<Float>(newTemp)

val observers = mutableListOf<TemperaturObserver>()

fun register(observer:TemperaturObserver) {
    observers.add(observer)
}

fun remove(observer: TemperaturObserver) {
    observers.remove(observer)
}

fun dataChanged() {
    observers.forEach {it.update(newTemp)}
}

fun messen() {
    var n = 100
    for (i in 0 until n) {
        newTemp = this.sensor.getTemperature()

        if(i != n) {
            dataChanged()
            tempwerte.add(newTemp)
        }
    }
}
fun getTenlastItems () = tempwerte.takeLast(10)
fun getHundredItems () = tempwerte.take (100)

the observer "weatherReport" should collect 10 items (temperature), print them and collect the next 10 items and so on

My solution

interface TemperaturObserver  {
fun update (newTemp : Float)

}

class WeatherReport (private var station : Thermometer) : TemperaturObserver {
override fun update (newTemp: Float) {
    var newList = mutableListOf<Float>(newTemp)

    while (newList.size != 10) {
    newList.add(newTemp)
    }
    println(newList)

}

}

creates this output

[40.0, 40.0, 40.0, 40.0, 40.0, 40.0, 40.0, 40.0, 40.0, 40.0]
[24.0, 24.0, 24.0, 24.0, 24.0, 24.0, 24.0, 24.0, 24.0, 24.0]

etc....

Any ideas how to solve the problem? It should be like that:

[21.0, 23.0, 0.0, 1.0, 35.0, 4.0, 14.0, 3.0, 16.0, 36.0]
[22.0, 27.0, 21.0, 32.0, 20.0, 31.0, 37.0, 33.0, 24.0, 2.0]

etc...

Thanks!